LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


Class 


"Westminster"  Series 


IRON    AND    STEEL 


Of    THF 

UNIVERSITY 

OF 


A  Scotch  Blast  Furnace  Plant,  Carron  Works. 


IRON    AND    STEEL 


BY 


J.   H.   STANSBIE,   B.Sc.  (Lond.)   F.I.C. 

ASSOCIATE      OF      MASON      UNIVERSITY      COLLEGE,      AND      LECTURER 
IN    THE    IURMINGHAM    MUNICIPAL    TECHNICAL    SCHOOL 


Of   THSE 

UNIVERSITY 

.    " 


NEW    YORK 

D.    VAN    NOSTRAND    COMPANY 

23    MURRAY   AND    27    WARREN    STREETS 

1908 


9ENERAL 


OF    THE 

I    UNIVERSITY    ) 

OF 


PREFACE 


IRON  is  the  most  important  of  all  the  metals  that  have 
been  pressed  into  the  service  of  man,  which  is  due,  not  only 
to  its  great  abundance  in  Nature,  but  also  to  its  unique 
properties.  The  result  of  this  is  that  no  one  metal  has 
received  so  much  attention  from  both  practical  men  and 
scientists,  as  is  shown  by  the  fact  that  some  of  the  most 
prominent  men  in  Europe  and  America  are  investigating 
the  many  chemical  and  physical  properties  of  the  metal 
and  its  application  to  the  requirements  of  civilisation. 
Thus  an  enormous  mass  of  information  has  accumulated, 
and  is  to  be  found  in  original  papers  and  books.  Portions 
of  the  subject  are  still  in  their  youth  and  are  growing 
vigorously,  so  that  the  teacher  of  to-day  must  become  the 
student  of  to-morrow.  On  the  other  hand,  parts  of  it  are 
so  old  that  their  origin  is  lost  in  the  mists  of  time,  and  dates 
back  to  the  first  glimmerings  of  that  intelligence  which 
now  enables  man  to  utilise  to  the  fullest  extent  the  valuable 
properties  of  the  metal. 

Although  the  necessity  of  technical  instruction  for  the 
worker  in  metals  has  become  an  acknowledged  fact,  the 
question  of  what  form  it  shall  take  is  still  engaging  the 
attention  of  educationalists.  It  is  clear,  however,  that 
the  greater  the  knowledge  the  worker  has  of  the  material 


206435 


vi  PEEFACE. 

he  is  using,  the  more  satisfactory  will  be  the  result  of  his 
labour,  both  to  himself  and  to  the  community  he  serves. 
Therefore  the  aim  of  technical  instruction  should  be  to 
foster  intelligent  effort  to  the  utmost.  To  teachers  who 
have  assisted  in  the  growth  of  technical  education  in  this 
country,  and  have  come  into  contact  with  those  workers 
who  are  willing  to  take  advantage  of  it,  one  fact  stands  out 
clearly,  viz.,  that  a  very  large  proportion  of  technical 
students  come  to  the  work  more  or  less  tired  with  their 
daily  labour,  and  have  but  a  limited  time  to  devote  to  self- 
improvement.  This  requires  that  every  assistance  should 
be  given  to  their  efforts,  and  that  the  subjects  they  study 
should  be  as  self-contained  as  possible.  The  aim  should 
be  to  increase  the  general  capability  of  the  greatest  number, 
and  not  to  turn  out  a  few  highly  trained  men. 

In  the  works,  economy  of  material  and  labour  should  be 
the  first  aim,  and  nothing  can  conduce  so  much  to  this  as 
a  thorough  knowledge  of  the  material  itself. 

The  aim  of  this  book  is  to  give  as  comprehensive  a  view 
as  its  limits  will  permit  of  the  modern  aspects  of  iron  and 
steel  manufacture,  together  with  a  sufficient  account  of  its 
history  to  enable  the  reader  to  follow  its  march  of  progress. 
The  methods  of  producing  varieties  of  the  metal  suitable 
to  the  requirements  of  the  engineer,  foundryman  and 
mechanician  are  described  sufficiently  to  enable  the  user 
to  follow  the  producer  in  his  work,  and  thus  learn  the 
history  of  the  material  he  is  handling.  The  main  portion 
of  the  book  has  been  written  from  notes  used  for  courses 
of  lectures  on  iron  and  steel  manufacture  extending  over 
many  years,  and  has  been  brought  up  to  date  by  reference 
to  the  latest  books  and  papers  on  the  subject.  The  author 


PREFACE.  vii 

has,  therefore,  to  express  his  sincere  obligation  to  the 
many  authors  of  works  and  papers  on  the  subject,  and 
to  the  practical  men  with  whom  he  has  come  into  contact 
who  have  so  freely  given  him  information  that  can  only  be 
obtained  from  such  sources.  Throughout  the  iron  and 
steel  industry  both  master  and  man  are  always  willing  to 
give  of  their  best,  and  that  freely. 

The  diagrams  are  intended  to  assist  the  reader  in  following 
the  text,  and  are  not  to  be  regarded  as  working  drawings. 
Whenever  possible,  photographs  of  the  actual  apparatus  have 
been  introduced  to  supplement  the  drawings,  and  in  this 
connection  the  thanks  of  both  reader  and  author  are  due  to 
such  well-known  firms  as  Messrs.  Firth,  of  Sheffield ; 
Messrs.  Hickman,  and  Messrs.  Perry,  of  Bilston ;  Messrs. 
Avery,  of  Birmingham ;  Messrs.  Massey,  of  Manchester  ; 
the  Cambridge  Scientific  Instrument  Company,  and  the 
Carron  Company  of  Glasgow. 

The  thanks  of  the  author  are  also  due  to  the  Council  of 
the  Iron  and  Steel  Institute,  and  to  the  Committee  of  the 
Faraday  Society  for  permission  to  copy  diagrams  from 
original  papers  in  their  Proceedings.  He  is  also  grateful 
to  Messrs.  C.  K.  Clark  and  W.  H.  Juggins  for  assistance 
in  the  preparation  of  diagrams  and  in  reading  the  proof 
sheets. 

J.  H.  S. 

MUNICIPAL  TECHNICAL  SCHOOL, 
BIRMINGHAM. 

October,   1907. 


CONTENTS 


CHAP'  PAGE 

I.      INTRODUCTORY         ......  1 

^    „       II.       IRON    ORES,    COMBUSTIBLE     AND     OTHER    MATERIALS    USED    IN 

IRON    AND    STEEL    MANUFACTURE 14 

III.  PRIMITIVE    METHODS    OF   IRON    AND    STEEL    PRODUCTION            .  51 

IV.  PIG    IRON    AND    ITS    MANUFACTURE              .             .  67 
V.       THE    REFINING    OF    PIG    IRON    IN    SMALL    CHARGES    .             .             .116 

VI.       CRUCIBLE    AND    WELD    STEEL              ......  140 

VII.       THE    BESSEMER    PROCESS 156 

VIII.       THE    OPEN    HEARTH    PROCESS              ......  182 

IX.       MECHANICAL    TREATMENT    OF    IRON    AND    STEEL         .             -             .  214 

X.       PHYSICAL   AND   MECHANICAL    PROPERTIES  OF  IRON    AND  STEEL  254 

^        XI.       IRON    AND    STEEL    UNDER    THE    MICROSCOPE      ....  268 

XII.       HEAT    TREATMENT    OF    IRON    AND    STEEL              ....  284 

XIII.  ELECTRIC    SMELTING         .                                                                             •  319 

XIV.  SPECIAL    STEELS       . 

GLOSSARY           .......                                                    •  3o7 

INDEX                                                                                                  367 


LIST    OF    ILLUSTRATIONS 


A  SCOTCH  BLAST  FURNACE  PLANT  .         .         .     Frontispiece. 

1.  THE  THOMPSON  CALORIMETER          ......  25 

2.  CHARCOAL  PILE      .        . 31 

3.  THE  OTTO-HOFFMAN  COKE  OVEN 84 

4.  THE  DUFF-WHITFIELD  PRODUCER 40 

5.  IRON  SMELTING  IN  INDIA 53 

6.  THE  CATALAN  FORGE 55 

7.  THE  HIGH  BLOOMERY 58 

8.  THE  HUSGAFVEL  FURNACE       .......  60 

9.  BLAST  FURNACE  WITH  OPEN  TOP    ......  68 

10.  GJERS  CALCINING  KILN 72 

11.  MODERN  BLAST  FURNACE 75 

12.  WATER-COOLED  HOT-BLAST  TWYER           .....  78 

13.  BOTTOM  OF  BLAST  FURNACE  SHOWING  TWYERS  IN  POSITION  .  79 

14.  COWPER'S  HOT-BLAST  STOVE   .......  81 

15.  BLOWING  CYLINDER 83 

16.  A  MODERN  BLAST  FURNACE  PLANT  ......  85 

17.  CUP  AND  CONE        .........  91 

18.  MECHANICAL  CHARGING  APPARATUS 101 

19.  FRACTURES  OF  PIG  IRON 105 

20.  FOUNDRY  CUPOLA 113 

21.  SWEDISH  LANCASHIRE  HEARTH 117 

22.  DIAGRAM  OF  PUDDLING  FURNACE 123 

23.  WORKING  SIDE  OF  PUDDLING  FURNACE 126 

24.  THE  PERNOT  FURNACE 136 

25.  CEMENTATION  FURNACE  ........  142 


xii  LIST   OF  ILLUSTRATIONS. 


NO. 

26.  CRUCIBLE    FURNACE            ........  146 

27.  CRUCIBLE    STEEL    MELTING    AT    NORFOLK    WORKS,    SHEFFIELD    .  148 

28.  STYRIAN    OPEN   HEARTH    ........  150 

29.  CONCENTRIC    CONVERTER             .......  161 

30.  ECCENTRIC    CONVERTER    ........  162 

31.  TILTING    LADLE          .........  164 

32.  CASTING   LADLE          .........  164 

33.  CONVERTER   AND    CRANES    IN   BESSEMER   SHOP  .            .            .  168 

34.  BESSEMER    CONVERTER   IN    POSITION  .....  171 

35.  CONVERTER    BOTTOM    IN    REPAIRING    SHOP  ....  173 

36.  CASTING    BASIC    STEEL    AT    SPRING   VALE    WORKS          .  .  .  175 

37.  MOULDS    AND    CRANES    IN    BESSEMER    SHOP          ....  179 

38.  REGENERATIVE    OPEN    HEARTH,    DIAGRAM  ....  183 

39.  REGENERATIVE    OPEN    HEARTH    (TRANSVERSE    SECTION)      .  .  186 

40.  FRONT    VIEW    OF    REGENERATIVE    OPEN    HEARTH          .  .  .  188 

41.  WORKING    PLATFORM    OF    OPEN    HEARTH    FURNACES  .  .  .  191 

42.  TAPPING    SIDE    OF   OPEN    HEARTH   FURNACE        ....  194 

43.  CAMPBELL    TILTING    FURNACE    (DIAGRAM)  ....  205 

44.  TILTING   FURNACE    WITH   ELECTRIC    CHARGER  ....  207 

45.  THE    HELVE    HAMMER         .  .  .......  214 

46.  INTERIOR    OF    THE    CLAY    WHEEL    FORGE  .....  215 

47.  EXTERIOR   OF    THE    CLAY   WHEEL   FORGE  ....  217 

48.  STEAM    HAMMER         .........  219 

49.  A    STAND    OF    ROLLS  ........  222 

50.  REHEATING    OR    MILL    FURNACE  ......  223 

51.  MILD    STEEL    INGOT  ........  227 

52.  GAS-FIRED    REHEATING   FURNACE    OR   SOAKING   PITS  .  .  235 

53.  A    STAND    OF    THREE    HIGH    ROLLS     ......  241 

54.  BLOOMING    SHEARS  .........  243 

55.  RAIL    ROLLS       ..........  245 

56.  A   3,000-TON    HYDRAULIC    PRESS         ......  249 

57.  INTERIOR    OF    STEEL    ROLLING    MILL  .....  252 

58.  DIAGRAM    OF    TENSILE    TESTING    MACHINE  ....  257 

59.  TENSILE    TESTING    MACHINE    IN    POSITION  ....  258 

60.  TENSILE    TEST    PIECES       .  260 


LIST   OF  ILLUSTRATIONS.  xiii 

NO.  ,-AGK 

61.  SHACKLES   FOR   CRUSHING    TESTS 261 

62.  DIAGRAM    OF   TRANSVERSE    TESTING    MACHINE  ....  262 

63.  TRANSVERSE    TESTING    MACHINE 263 

64.  PENDULUM   DROP   TEST    MACHINE 264 

65.  FERRITE 275 

66.  CEMENTITE       ..........  276 

67.  PEARLITE 277 

68.  AUSTENITE    AND    MARTENSITE              ......  278 

69.  GRAPHITE    AND    FERRITE 280 

70.  CAST    IRON    CONTAINING   SULPHUR 281 

71.  CAST    IRON    WITH    PHOSPHIDE    EUTECTIC  .                        ...  282 

72.  ANNEALED    AND    HARDENED    STEEL- 283 

73.  COOLING   CURVES    OF    COPPER   AND   IRON 285 

74.  COOLING    CURVE    OF    LEAD    TIN    ALLOYS 289 

75.  COOLING    CURVE    OF    SALT    SOLUTION            .....  291 

76.  COOLING    CURVES    OF    IRON    CARBON    ALLOYS       ....  297 

77.  THE    ROBERTS-AUSTEN-ROOZEBOOM    CURVE          .             .             .  299 

78.  MUFFLE    FURNACE •             •  304 

79.  RESISTANCE    PYROMETER 313 

80.  RADIATION    PYROMETER    ........  316 

81.  ALTERNATORS    IN    POSITION 321 

82.  THE    HEROULT    FURNACE 327 

83.  THE    HEROULT    FURNACE    IN    POSITION        ...                          .  329 

84.  THE    KJELLIN    FURNACE    ....                          ...  330 

85.  THE    STASSANO    FURNACE 

86.  THE    KELLER    FURNACE 337 


OF   THE 

UNIVERSITY 

OF 


IRON    AND    STEEL 


CHAPTER   I. 

INTRODUCTORY. 

PURE  IRON  belongs  to  a  class  of  bodies  composed  of 
substance  or  matter  which  is  as  simple  in  character  as  it 
can  possibly  be.  These  simple  bodies  are  the  elements 
which  enter  into  the  composition  of  all  the  more  complex 
bodies  that  form  the  crust  of  the  earth,  the  water  which 
covers  the  greater  part  of  it,  and  the  atmosphere  that 
surrounds  it  on  all  sides.  The  number  of  elements  is 
small,  but  the  number  of  complex  bodies  formed  from 
them  is  very  large,  for  the  elements  bear  somewhat  the 
same  relation  to  the  other  bodies  into  the  composition  of 
which  they  enter,  as  do  the  letters  of  the  alphabet  to  the 
words  of  the  language  of  which  they  form  a  part. 

The  distinctive  properties  of  the  elements  enable  them 
to  be  arranged  in  two  groups,  of  which  the  pure  metals 
form  the  largest.  The  general  properties  of  the  metals  are 
so  characteristic  that  there  is  no  difficulty  in  recognising 
them  by  simple  inspection.  The  members  of  the  other 
group  have  properties  so  distinctly  opposite  to  those  of  the 
metals  that  for  the  want  of  a  better  name  they  are  termed 
non-metals.  Such  well-known  substances  as  sulphur, 
phosphorus,  and  carbon  are  non-metals.  Compare,  for 
example,  a  piece  of  iron  with  a  piece  of  charcoal,  and  the 

i.s.  B 


2  IEON  AND  STEEL. 

difference  between  a  metal  and  a  non-metal  becomes  quite 
evident.  A  few  elements,  however,  are  very  close  to  the 
border  line  between  the  two  groups  ;  but  these  need  not  be 
discussed  here.  The  well-known  elements  exist  in  different 
physical  states  under  ordinary  atmospheric  conditions : 
thus,  four  are  gases,  oxygen,  hydrogen,  nitrogen,  and 
chlorine ;  two  are  liquids,  mercury  and  bromine ;  the  re- 
mainder are  well  denned  solids.  A  table  of  those  elements 
with  which  the  reader  should  be  more  or  less  acquainted 
will  be  found  on  p.  13. 

The  rusting  of  iron  is  one  of  the  well  known  properties 
of  the  metal,  and  there  are  few  who  have  not  noticed  the 
very  characteristic  change  that  takes  place  during  the 
process ;  the  difference  between  the  dark  red  rust  and  the 
metal  from  which  it  is  formed  is  so  very  marked.  Why  does 
iron  rust  ?  To  answer  this  question  it  is  necessary  to  refer 
briefly  to  the  nature  and  composition  of  air.  A  good 
working  atmosphere  is  a  mixture  of  four  gases — oxygen, 
nitrogen,  carbon  dioxide  and  water  vapour,  of  which  the 
oxygen  and  nitrogen  form  respectively  about  one-fifth  and 
four-fifths  of  the  main  bulk.  These  gases  are  elements, 
but  the  carbon  dioxide  and  water  vapour  are  complex 
bodies  or  compounds.  Now  the  rusting  process,  as  it  takes 
place  under  ordinary  circumstances,  depends  upon  the 
presence  of  oxygen  and  condensed  water  vapour.  A  piece 
of  bright  iron  exposed  to  the  air  will  not  begin  to  rust  until 
water  vapour  condenses  to  the  liquid  state  on  its  surface. 
Then  an  action  is  set  up ;  oxygen  is  absorbed  from  the  air, 
and  the  rusting  goes  on  slowly  but  surely.  When  perfectly 
dry  rust  is  strongly  heated,  water  is  driven  off  and  a  red 
powder  is  left  behind.  This  shows  that  water  takes  part 
in  the  change,  and  enters  into  the  composition  of  the  rust. 
The  red  powder  obtained  by  strongly  heating  the  rust  is 
found  to  contain  iron  and  oxygen  only,  to  contain  these 
elements  in  definite  ^ind  invariable  proportions,  and  to 


INTRODUCTORY.  3 

differ  entirely  in  properties  from  the  elements  which  enter 
into  its  composition.  These  are  the  characteristics  of  a 
given  chemical  compound,  which  always  contains  the  same 
elements  in  the  same  proportions.  The  red  powder  is 
red  oxide  of  iron,  a  definite  body  of  invariable  composition. 

If  a  piece  of  iron  is  kept  in  the  fire  for  some  time  a 
black  scale  forms  on  its  surface.  This  scale  can  be  scraped 
off  and  ground  to  a  fine  powder,  and  is  very  different  from 
the  metal  from  which  it  is  formed.  It  contains  a  definite 
proportion  of  oxygen  which  it  has  obtained  from  the  air 
passing  through  the  fire.  The  proportions  of  iron  and 
oxygen  are,  however,  different  from  those  in  the  rust,  so 
that  a  different  body  is  obtained.  It  is  another  chemical 
compound  of  iron  and  oxygen. 

When  an  element  unites  with  oxygen  to  form  a  chemical 
compound,  the  compound  so  formed  is  called  an  oxide. 
The  red  rust  and  black  scale  are  then  oxides  of  iron,  and 
the  difference  between  them  is  due  to  the  difference  in  the 
proportions  of  the  two  elements  they  contain,  and  to  that 
only.  All  the  elements  that  will  be  noticed  in  these  pages 
unite  with  oxygen  to  form  one  or  more  oxides,  so  that  the 
oxides  are  a  most  important  class  of  bodies. 

It  is  easy  to  find  by  actual  experiment  the  proportions 
of  the  two  elements  in  any  oxide.  These  proportions  can 
then  be  stated  as  a  percentage  composition,  that  is,  so 
many  parts  of  each  element  in  100  parts  of  the  compound. 
Thus  the  red  oxide  contains  70  parts  of  iron  and  30  parts 
of  oxygen ;  and  the  black  oxide  72'4  parts  of  iron  and  27*6 
parts  of  oxygen  in  100  parts  of  the  compounds. 

But  chemists  have  devised  a  much  more  convenient  way 
of  representing  the  composition  of  compounds.  The  com- 
bining proportions  of  all  elements  are  compared  with  the 
combining  proportion  of  hydrogen,  which  has  the  smallest 
combining  proportion  of  any  known  element.  This  allows 
of  the  elements  being  arranged  in  a  tabular  form  according 

B  2 


4  IEON  AND   STEEL. 

to  their  combining  proportions.  It  is  to  be  distinctly 
understood  that  the  numbers  representing  these  combining 
proportions,  or  chemical  equivalents,  are  the  results  of  direct 
experiments,  and  the  only  assumption  made  is  that  there 
are  such  things  as  elements,  and  that  they  combine  together 
to  form  compounds. 

It  has,  however,  been  found  more  convenient  to  use  the 
Atomic  Theory  of  Dalton  in  fixing  these  proportional 
numbers  for  the  elements  generally.  This  theory  assumes 
that  sensible  masses  of  all  definite  bodies,  either  elements 
or  compounds,  are  made  up  of  exceedingly  small  particles 
called  molecules,  and  that  these  molecules  are  again  made 
up  of  still  smaller  particles  called  atoms.  Now  molecules 
are  supposed  to  be  the  smallest  possible  particles  of  either 
elements  or  compounds  which  can  have  a  free  existence, 
and  atoms  are  the  smallest  particles  of  elements  which  can 
exist  at  all.  It  must  be  carefully  borne  in  mind  that 
molecules  are  the  smallest  possible  particles  of  compounds, 
and  the  smallest  particles  of  free  elements. 

Now  the  one  invariable  property  of  matter  or  substance 
is  its  mass,  which  is  usually  measured  by  weight ;  so  that 
atoms,  however  small  they  may  be,  must  have  mass  and 
therefore  weight.  The  term  atomic  weight  is,  therefore, 
justifiable.  A  number  of  considerations,  which  cannot 
be  entered  into  here,  are  taken  into  account  in  fixing  the 
atomic  weight  of  an  element,  but  the  first  is  always  the 
combining  proportion  as  Determined  by  experiment,  and  it 
is  found  that  a  very  simple  relation  exists  between  the 
combining  proportion  of  an  element  and  its  atomic  weight. 
The  atomic  weight  of  an  element  is  either  the  same  as  its 
combining  proportion  or  a  simple  multiple  of  it. 

In  thinking  of  atoms  their  weights  must  be  recognised, 
and  if  atoms  are  represented  by  symbols,  such  symbols 
will  also  represent  their  weights.  Thus  the  symbol  for 
iron  is  Fe,  taken  frorn^the  Latin  name  Ferrum,  so  that  Fe 


INTRODUCTORY.  5 

means  the  same  as  the  phrase  "  one  atom  of  iron,"  and  is 
a  ready  way  of  stating  it.  Also,  Fe  =  5(>  means  that  the 
atomic  weight  of  iron  is  56  compared  with  the  atomic 
weight  of  hydrogen,  which  is  H  =  l.  Similarly,  the 
symhol  and  atomic  weight  of  oxygen  are  expressed  thus  : 
0  =  16. 

Now,  if  it  is  assumed  that  a  given  weight  of  iron  is  made 
up  of  a  definite,  although  very  large,  number  of  atoms, 
that  weight  divided  by  the  atomic  weight  of  the  metal  will 
give  a  quotient  which  is  proportional  to  the  number  of 
atoms  of  iron  in  the  mass.  Similarly,  a  given  weight  of 
oxygen  divided  by  its  atomic  ^weight  will  give  a  number 
proportional  to  the  number  of  atoms  in  the  mass.  It  is 
proved  by  experiment  that  red  oxide  of  iron  contains  70 
parts  by  weight  of  iron  and  30  parts  by  weight  of  oxygen 
in  100  parts  by  weight  of  the  compound,  and  if  these 
weights  are  divided  by  the  atomic  weights  of  the  elements, 
thus:— 

jg  =  T25,  and  ^  =  1-876 
ob  ID 

it  is  easily  seen  that  the  ratio  1*25  to  1*875  is  the  same  as 
the  ratio  2  to  3,  so  that  must  be  the  proportion  between  the 
number  of  atoms  of  iron  and  the  number  of  atoms  of 
oxygen  in  the  molecules  of  the  red  oxide  of  iron.  This  is 
shown  by  arranging  the  symbols  together  thus  :  Fe^Oa, 
which  represents  the  composition  of  the  oxide  according  to 
the  atomic  theory,  and  is  called  the  formula  of  the  com- 
pound. Similarly  the  black  oxide  contains  72'4  parts  of 
iron  and  27*6  parts  of  oxygen  in  100  parts. 

Therefore,    ^  =   T292,  and  ^  -   T729 
56  lo 

so  that  the  ratio  T292  to  T729  is  very  nearly  the  same 
as  3  to  4,  or  the  formula  for  the  oxide  is  FeaO^. 


6  IRON  AND  STEEL. 

There  are  two  ways  of  regarding  these  symbols  and 
formulae :  the  theoretical  way,  in  which  they  represent 
atoms  of  elements  and  molecules  of  elements  and  com- 
pounds ;  and  the  practical  way,  in  which  they  represent  the 
composition  in  definite  parts  by  weight  of  the  definite 
bodies  under  consideration.  Thus  100  tons  of  iron  scale 
contain  72  tons  8  cwts.  of  iron  and  27  tons  12  cwts.  of 
oxygen.  This  appeals  most  to  the  practical  man;  but 
that  is  not  to  say  that  it  is  not  as  well  to  take  the  other 
view  sometimes. 

The  chemist  also  uses  these  symbols  and  formulae  to 
represent  in  a  connected  manner  the  chemical  changes 
taking  place  when  compound  bodies  are  either  formed  or 
decomposed.  Thus,  when  the  iron  scale  is  forming  in  the 
fire  the  molecules  of  oxygen  in  the  air  taking  part  in  the 
change  may  be  pictured  as  dividing  up  into  atoms,  and 
these  atoms  linking  themselves  with  the  atoms  of  iron  to 
form  the  oxide.  Further,  two  molecules  of  oxygen  are 
supposed  to  break  up  into  four  atoms,  and  these  to  link 
with  three  atoms  of  iron  to  form  one  molecule  of  the  oxide. 
This  may  be  expressed  graphically  thus  :  — 

3Fe        +        202       =      Fe304 
3  Atoms.          2  Molecules.         1  Molecule. 

and  it  may  be  predicted  that  what  takes  place  in  this 
group  also  takes  place  in  every  other  similar  group  in  the 
whole  mass  undergoing  the  change.  This  is  strongly  sup- 
supported  by  the  fact  that  the  statement  is  proved  by 
experiment,  for 

BFe    +    202  =  Fe304 

56  X  3       16  X  4          232 

expresses  exactly  how  much  oxygen  will  be  absorbed  from 
the  air  by  a  given  weight  of  iron  during  its  conversion 
into  scale.  This  formulated  statement  of  fact  and  theory 
is  a  chemical  equation.  Such  equations  are  found  very 


INTEODUCTORY.  7 

useful  in  following  the  chemical  changes  and  in  calculating 
the  weights  of  materials  taking  part  in  various  operations. 

The  element  next  in  importance  to  the  iron  and  steel 
maker  is  the  non-metal  carbon,  which  is  the  principal 
combustible  constituent  of  the  combustible  bodies  wood, 
coal,  charcoal,  and  coke.  If  carbon  is  to  burn  vigorously 
it  must  be  well  supplied  with  air,  and  the  chemical 
change  that  takes  place  is  exactly  similar  to  the  formation 
of  iron  scale,  for  it  consists  of  the  rapid  absorption  of 
oxygen  from  the  air,  and  the  formation  of  an  oxide  of 
carbon  ;  but  this  oxide  is  a  gas  and  escapes  into  the  space 
surrounding  the  burning  body  as  fast  as  it  is  formed.  It 
may,  however,  be  collected  in  suitable  apparatus  and 
weighed,  and  is  then  found  to  contain  carbon  and  oxygen 
in  definite  proportions.  It  is  carbon  dioxide,  COo.  The 
change  is  expressed  by  an  equation  thus  :— 

C  +   02  =  C02. 

12       16  X  2      44 

This  may  be  read  as  follows  :  one  atom  or  12  parts  by 
weight  of  carbon,  and  one  molecule  or  32  parts  by 
weight  of  oxygen  furnish  one  molecule  or  44  parts  by 
weight  of  carbon  dioxide ;  or,  taking  concrete  quantities, 
12  cwts.  of  carbon  and  1  ton  12  cwts.  of  oxygen  furnish 
2  tons  4  cwts.  of  carbon  dioxide,  together  with  a  large, 
but  just  as  definite,  quantity  of  heat. 

But  when  carbon  is  burning  at  a  very  high  temperature 
in  a  current  of  hot  air,  only  half  the  oxygen  is  absorbed, 
and  a  lower  oxide  of  carbon  formed,  thus  :— 
20    +    02   =      2CO. 

12  X  2       16  X  2         06 

This  gas  is  known  as  carbon  monoxide  and  is  combustible, 
for  it  can  absorb  more  oxygen  and  be  converted  into  the 
higher  oxide.  It  takes  a  very  important  part  in  the 
manufacture  of  iron  and  steel. 


8  IEON  AND   STEEL. 

Carbon  dioxide  is  found  associated  with  another  oxide 
of  iron  still  richer  in  iron  than  the  two  already  described. 
It  is  represented  by  the  formula  FeO,  which  shows  that  it 
contains  56  parts  of  iron  to  16  parts  of  oxygen ;  or  77*7 
per  cent,  of  iron  and  22'3  per  cent,  of  oxygen.  The  two 
oxides  combine  to  form  a  compound  which  has  the  formula 
FeO.COs,  and  is  known  as  ferrous  carbonate,  a  most 
important  natural  compound  of  the  metal. 

It  will  be  noticed  that  ferrous  carbonate  is  made  up  of 
two  oxides,  one  an  oxide  of  a  metal  and  the  other  an  oxide 
of  a  non-metal.  Now  these  oxides  are  representatives  of 
two  classes  of  oxides  :  (1)  the  oxides  of  the  metals,  with  a 
few  exceptions,  are  known  as  basic  oxides ;  (2)  the  oxides 
of  the  non-metals,  with  some  exceptions,  are  known  as 
acid-forming  oxides.  The  acid-forming  oxides  generally 
unite  with  water  to  form  acids.  Water  itself  is  an  oxide  of 
the  non-metal  hydrogen,  and  contains  2  parts  by  weight  of 
hydrogen  to  16  parts  by  weight  of  oxygen,  so  that  its 
formula  is  written  H20. 

The  most  widely  occurring  and  best  known  acid-forming 
oxide  is  silica,  which  is  the  only  oxide  of  the  non-metal 
silicon.  It  occurs  in  the  pure  form  in  the  transparent 
colourless  crystals  of  quartz,  and  in  a  less  pure  form  in 
silica  sand.  It  is  also  a  constituent  of  a  large  number  of 
rocks  in  the  earth's  crust.  The  atomic  weight  of  silicon  is 
28,  and  the  oxide  contains  silicon  and  oxygen  in  the  pro- 
portion of  28  to  32,  so  that  its  formula  is  Si02.  It 
combines  with  the  basic  oxides  to  form  a  class  of  well-known 
compounds,  the  silicates ;  but  the  combination  only  takes 
place  at  a  high  temperature.  Some  of  the  simple  silicates 
melt  at  a  red  heat;  others  require  a  very  much  higher 
temperature.  But  if  two  or  more  basic  oxides  are  present 
with  the  silica  so  as  to  form  a  complex  silicate,  the  melting 
point  of  the  mass  is  always  lower  than  the  melting  point  of 
the  most  infusible  silicate  in  it,  These  facts  are  taken 


INTKODUCTOKY.  9 

advantage  of  in  separating  infusible  siliceous  matter  during 
the  processes  of  iron  and  steel  manufacture. 

The  most  important  silicates  met  with  in  the  processes 
and  materials  to  be  described  later  are  the  silicates  of 
ferrous  oxide,  FeO ;  lime,  CaO ;  magnesia,  MgO ;  and 
alumina,  AlaOg. 

Another  important  acid-forming  oxide  is  phosphoric 
oxide,  P205,  which  is  always  formed  when  phosphorus 
burns  in  air  or  oxygen.  It  combines  readily  with  basic 
oxides  to  form  phosphates,  a  well-known  class  of  com- 
pounds. Phosphorus  also  unites  with  many  of  the  metals 
to  form  phosphides. 

Sulphur  is  another  non-metal  that  makes  itself  very 
evident  in  the  metallurgy  of  iron.  It  has  a  powerful 
affinity  for  the  metal,  and  combines  with  it  readily  at  a 
moderate  temperature.  If  a  mixture  of  fine  iron  filings 
and  powdered  sulphur  is  heated  until  the  latter  begins  to 
melt,  rapid  combination  of  the  two  elements  takes  place 
with  the  liberation  of  much  heat,  and  the  mass  is  raised  to 
a  bright  red  heat  without  any  further  heating  from  outside. 
Iron  burns  in  sulphur  vapour  in  much  the  same  way  that 
it  burns  in  oxygen.  The  properties  of  the  resulting  com- 
pound are  quite  distinct  from  those  of  the  elements  that 
enter  into  its  composition.  The  chemical  change  and  the 
weight  relations  are  expressed  by  the  equation — 

Fe  +  S  =  FeS. 

56          32  88 

The  compound  ferrous  sulphide  is  the  stable  sulphide  of 
iron.  Others  will  be  mentioned  later,  but  this  is  the  most 
important  one  to  the  iron  metallurgist.  The  presence  of  a 
small  quantity  of  it  in  commercial  iron  renders  the  metal 
unworkable  at  a  red  heat.  Sulphur  itself  is  a  yellow, 
crystalline  solid  that  melts  readily  when  heated,  and  burns 
with  a  blue  flame  in  air  or  oxygen.  The  compound  formed 


10  IEON   AND   STEEL. 

in  the  burning  is  sulphur  dioxide,  S02 ;  but  there  is 
another  compound,  sulphur  trioxide,  S03,  which  is  the 
principal  acid  forming  oxide  of  sulphur,  and  is  present  in 
sulphuric  acid,  H^SO^ 

Water  plays  a  most  important  part  in  several  of  the 
reactions  and  processes  to  be  considered  later.  It  is  an 
oxide  of  hydrogen,  and  is  formed  when  the  gas  hydrogen, 
or  any  combustible  body  containing  it,  is  burnt  in  air  or 
oxygen.  Much  heat  is  developed  by  the  combustion,  and 
the  change  is  represented  thus  : — 

2H2  +  02  -  2H20. 

4  32  36 

By  dividing  each  of  the  proportional  weights  by  4  it  is 
seen  that  1  part  by  weight  of  hydrogen  combines  with  8 
parts  by  weight  of  oxygen  to  form  9  parts  by  weight  of 
water. 

Hydrogen  will  also  remove  the  oxygen  of  some  metallic 
oxides  when  they  are  heated  in  its  presence,  and  thus  set 
the  metals  free.  This  action  is  spoken  of  as  reduction,  and 
the  gas  itself  as  the  reducing  agent.  If  hydrogen  is  passed 
through  a  glass  tube  in  which  some  red  oxide  of  iron  is 
being  heated  to  a  dull  red  heat,  the  red  colour  of  the  oxide 
disappears,  and  water  collects  in  a  receiver  connected  with 
the  exit  end  of  the  tube.  The  black  powder  left  in  the 
tube  is  found  to  be  finely  divided  metallic  iron.  The 
change  is  thus  expressed  :— 

Fe203  +  3H2  =  2Fe  +  3H20. 

160  6  112  54 

Carbon,  C,  and  carbon  monoxide,  CO,  will  also  remove  the 
oxygen  from  metallic  oxides  when  heated  in  contact  with 
them,  and  in  the  case  of  oxides  of  iron  the  reduction  takes 
place  at  a  comparatively  low  temperature.  Thus,  if  carbon 
monoxide  gas  is  substituted  for  hydrogen  in  the  experiment 
described  above,  metallic  iron  is  slill  obtained,  but  it  is 


INTRODUCTORY.  1 1 

found  to  have  reacted  on  the  excess  of  the  monoxide,  and  to 
have  absorbed  some  carbon  from  it.  The  change  is  as 
follows  :— 

Fe203  +  SCO  -  2Fe  +  3C02. 

If  a  mixture  of  powdered  charcoal  and  oxide  of  iron  is 
made  red  hot,  the  carbon  of  the  charcoal  unites  with  the 
oxygen  of  the  oxide,  and  iron  is  set  free.  It  is  in  a  finely 
divided  state,  and  must  not  be  exposed  to  the  air  while  it  is 
hot,  or  it  will  oxidise  again  very  rapidly.  The  change  is— 

2Fe203  +  3C  =  4Fe  +  3C02. 

The  atmosphere  which  surrounds  the  earth  is  so  essential 
to  life  that  we  become  familiar  with  it  at  an  early  age,  and 
learn  to  recognise  it  by  its  general  properties.  It  is  a 
mixture  of  gases  of  which  two,  oxygen  and  nitrogen,  are 
regarded  as  the  essential  constituents.  Oxygen  is  the  sup- 
porter of  combustion,  and  enters  into  all  oxidation  changes. 
If  used  in  the  pure  state,  all  such  changes  take  place  much 
more  rapidly  and  energetically  than  when  it  is  diluted  by 
the  presence  of  nitrogen,  which  is  an  inert  gas.  In  fact,  the 
chief  function  of  nitrogen  in  the  atmosphere  is  to  modify  the 
action  of  the  oxygen  by  diluting  it.  The  oxidation  processes 
by  which  carbon  dioxide  is  formed  are  largely  responsible 
for  the  presence  of  the  gas  in  the  atmosphere  ;  but  as  this 
gas  is  absorbed  by  growing  plants,  a  more  or  less  rough 
balance  is  struck,  and  the  proportion  of  carbon  dioxide  in 
the  atmosphere  is  fairly  constant.  Water  vapour  is  also  a 
constant  constituent  of  the  atmosphere,  into  which  it  passes 
from  the  large  bodies  of  water  in  contact  with  it.  But  the 
proportion  present  varies  considerably  from  time  to  time, 
as  it  depends  upon  a  number  of  conditions,  the  principal 
one  of  which  is  temperature.  The  higher  the  temperature 
of  the  air,  the  more  water  vapour  it  will  absorb ;  but  the 
saturation  point  is  rarely  reached. 


12  IRON  AND   STEEL. 

The  following  may  be  taken  as  an  average  composition 
by  volume  of  atmospheric  air1  :— 

Oxygen,  02         ......  20'66 

Nitrogen,  N2 77'91 

Carbon  dioxide,  C02            ....  0'03 

Water  vapour,  H20 T40 

100-00 

The  most  important  physical  and  mechanical  properties 
of  the  atmosphere  are  due  to  its  temperature  and  pressure, 
both  of  which  are  variable.  The  general  tendency  of  lower- 
ing the  temperature  of  gases  and  vapour  is  towards  changing 
them  into  liquids,  and  finally  into  solids ;  but  the  ordinary 
changes  in  the  atmosphere  have  very  little  effect  upon  its 
gases,  with  the  exception  of  water  vapour.  Liquid  water 
separates  from  the  air  when  its  temperature  falls  below  the 
saturation  point  of  its  contained  water  vapour ;  but  even  a 
considerable  reduction  in  the  temperature  only  effects  a 
partial  separation  of  the  water  from  air.  The  familiar 
phenomenon  of  dew  and  rain  are  the  results  of  this  con- 
densation, which  can  also  be  effected  artificially,  so  that  it 
is  possible  to  regulate  the  quantity  of  water  vapour  in  air  to 
be  used  for  manufacturing  purposes  by  cooling  it  before  use. 
The  barometric  pressure  of  the  air  also  varies  considerably 
from  time  to  time,  so  that  a  standard  pressure  is  adopted 
for  comparison.  This  is  equal  to  the  pressure  of  a  column 
of  mercury  29'92  inches,  or  760  millimetres  high.  This  is 
equal,  roughly,  to  a  direct  pressure  of  15  pounds  on  the 
square  inch  of  surface  exposed  to  it ;  but  in  still  air  this 
pressure  is  exerted  equally  in  all  directions,  and  is  not 
noticeable,  although  it  can  be  measured  by  causing  it  to 
balance  a  column  of  mercury  as  indicated  above.  But  air 
in  motion  through  pipes  has  a  pressure  greater  than  this, 
and  the  excess  of  pressure  depends  upon  the  driving  force 

1  Small  quantities -of   several  gases,  of  which,  argon  is   the  most 
important,  are  also  present  in  the  atmosphere. 


INTRODUCTORY. 


producing  the  motion.  The  greater  the  excess  of  pressure 
the  more  rapid  the  motion,  and  the  greater  the  quantity  of 
air  passing  through  a  given  cross-section  in  unit  time. 
Such  excess  pressures  are  usually  stated  in  pounds  per 
square  inch,  and  may  vary  in  ordinary  furnace  practice 
from  a  few  ounces  to  twenty-five  pounds  per  square  inch. 

TABLE  OF  SOME  COMMON  ELEMENTS  AND  OXIDES. 
Non-Metals. 


Elements. 

Symbols. 

Atomic 
Weights. 

Oxides. 

Formula-. 

Common  Names. 

Arsenic 

As 

75 

Arsenic  Trioxide 

As20» 

White  Arsenic. 

Bromine 

Br 

80 

Carbon 

C 

12 

Carbon  Monoxide     . 

CO 

Carbonic  Oxide. 

„       Dioxide 

C02 

,,         Acid  Gas. 

Chlorine 

Cl 

35-5 

Hydrogen 

H 

1 

Hydrogen  Monoxide 

H20 

Water. 

Iodine  . 

I 

126-5 

Nitrogen 

N 

14 

Nitrogen  Dioxide 

NO 

Nitric  Oxide. 

,,         Tetroxide  . 

NO-2 

,,     Peroxide. 

Oxygen 

O 

16 

Phosphorus 
Silicon 

P 

Si 

31 

Phosphoric  Oxide     . 
Silicon  Dioxide 

P206 

SiO-2 

Phosphoric  Acid. 
Silica. 

Sulphur 

S 

32 

Sulphur  Dioxide 

SOa 

„         Trioxide     . 

SO8 

Metals. 


Aluminium  . 

Al 

27 

Aluminium  Oxide    . 

A12OH 

Alumina. 

Calcium 

Ca 

40 

Calcium  Oxide. 

CaO' 

Lime. 

Chromium  . 

Cr 

52-5 

Chromium  Oxide 

CnjOj. 

Chromic  Oxide. 

Copper 

Cu 

63 

Cupric  Oxide    .        .        CuO 

Black     Oxide     of 

Copper. 

Cuprous  Oxide          .        Cu2O 

Red  Oxide  of  Copper. 

Iron 

Fe 

56 

Ferrous  Oxide  . 

FeO 

Triferric  Tetroxide  . 

Fe«O4 

Black  Oxide  of  Iron. 

Ferric  Oxide     .        .   I     Fe2O.s 

Red  Oxide  of  Iron. 

Lead     . 

Pb 

207 

Lead  Oxide 

PbO 

Massicot  or  Litharge. 

Triplumbic        Tetr- 

Pb»o4 

Red  Lead. 

oxide 

Magnesium  . 

Mg 

24 

Magnesium  Oxide    .        MgO 

Magnesia. 

Manganese  . 

Mn 

55 

Manganous  Oxide    .        MnO 

Manganese  Dioxide  .        MnO2 

Black  Oxide  of  Man- 

ganese. 

Molybdenum 

Mo 

96           Molybdenum        Tri-  !     MoO;! 

Molybdic  Acid. 

oxide      . 

Nickel. 

Ni 

58-6         Nickel  Oxide    . 

NiO 

Titanium     . 

Ti 

48           Titanium  Oxide        .        TiO-2 

Tin       . 

Sn 

118 

Stannic  Oxide  .        .        SnOa 

Tin  Oxide. 

Tungsten     . 

W 

183-6 

Tungsten  Trioxide   . 

WOS 

Tungstic  Acid. 

Vanadium    . 

V 

51 

Vanadium  Pentoxide 

V20r) 

Zinc     . 

Zn 

65 

Zinc  Oxide 

ZnO 

Zinc  White. 

CHAPTEK   II. 

IRON    ORES,    COMBUSTIBLE    AND    OTHER    MATERIALS    USED    IN 
IRON    AND    STEEL    MANUFACTURE. 

THE  earth's  crust  is  the  storehouse  from  which  come  the 
solid  materials  used  in  making  iron  and  steel ;  and  the 
occurrence,  distribution,  and  properties  of  such  materials 
may  now  be  considered.  The  formation  of  the  crust  of  the 
earth,  as  far  as  it  is  known  to  man,  can  be  traced  to  the 
action  of  well-known  forces,  and  may  be  said  to  have  begun 
when  the  temperature  of  the  cooling  solid  crust  was  such 
that  water  vapour  in  the  atmosphere  surrounding  it  began  to 
condense  and  fall  as  rain  drops  on  the  surface.  The  various 
atmospheric  influences,  such  as  wind  and  rain  and  alterna- 
tions of  heat  and  cold,  commenced  the  breaking  up  of  the  solid 
structure,  and  the  transport  of  the  deltris  from  one  part  to 
another.  The  same  agents  are  working  to-day,  slowly  and 
surely,  and  from  their  present  action  the  geologist  is  able 
to  draw  deductions  as  to  what  took  place  during  the  long 
periods  of  time  in  which  the  rocks  with  which  he  is 
acquainted  were  formed.  The  formation  of  stratified  rocks 
is  due  to  atmospheric  agencies,  assisted  by  running  water, 
which,  if  allowed  to  work  undisturbed,  would  gradually 
reduce  the  surface  to  one  dead  level ;  but  forces  working  in 
the  crust  itself  have  to  be  considered,  for  the  gradual 
cooling  of  the  earth's  mass,  with  its  accompanying  shrinkage, 
has  broken  up  the  surface  into  vast  ridges  and  hollows, 
forming  mountain  chains  and  ocean  beds. 

By  careful  examination  of  stratified  rocks,  all  the  world 
over,  geologists  have  loeen  able  to  classify  them  into  well- 


MATEEIALS  USED  IN  IEON  AND  STEEL  MANUFACTUEE.  lo 

marked  systems.  The  presence  of  a  given  stratified  rock, 
or  system  of  rocks,  presupposes  that  the  underlying  rock 
was  under  water  during  its  formation  ;  so  that  whether  a 
particular  rock  or  system  is  present  in  the  crust  of  a  given 
district  depends  upon  whether  that  district  was  submerged 
or  not  during  the  period  when  such  rocks  were  in  course 
of  formation.  If,  then,  certain  metalliferous  minerals  are 
known  to  be  associated  with  a  particular  system  of  rocks,  it 
is  evidently  necessary  to  find  out  if  that  system  is  repre- 
sented in  the  strata  of  the  district  before  commencing  the 
search  for  such  minerals  there  ;  but  the  practical  man  of 
the  past  was  not  always  educated  up  to  this  point,  and 
much  money  and  labour  have  been  expended  in  vain. 

The  stratified  rocks  in  various  parts  of  the  crust  have 
been  disturbed  and  altered  by  the  intrusion  of  molten 
matter  from  below  from  which  the  igneous  rocks  have  been 
formed.  The  granites  and  similar  rocks  are  of  igneous  origin. 
It  is  well  known  that  the  useful  metals  are  associated  for 
the  most  part  with  the  older  rocks,  and  the  seeker  for  such 
metals  usually  makes  for  the  hills  where  these  rocks  have 
been  brought  to  the  surface  during  the  crumpling  process 
by  which  the  hills  were  formed.  It  must  not  be  thought 
from  this  that  every  mountain-side  will  furnish  a  store  of 
metalliferous  matter,  but  in  portions  of  most  mountain 
ranges  all  over  the  world  some  of  the  useful  metals  are  to 
be  found.  Although  the  common  metals  are  very  widely 
distributed  through  the  earth's  crust,  it  is  only  when  they 
have  become  concentrated  in  veins,  beds,  or  irregular 
deposits  of  considerable  extent  that  they  pay  for  getting. 
Also,  during  the  weathering  of  rocks  on  the  mountain-side, 
and  the  transport  of  broken  material  by  mountain  streams 
and  rivers,  with  the  deposition  of  finely  divided  matter 
in  the  beds  of  lakes  and  the  estuaries  of  rivers,  a  selective 
process  took  place,  and  layers  of  different  materials  were 
deposited  one  over  the  other  to  form  stratified  rocks.  In 


16  IRON  AND  STEEL. 

this  manner  rich  metalliferous  deposits   may   have   been 
formed  in  positions  far  removed  from  the  hills. 

Very  few  metals  are  found  in  the  metallic,  or  "  native  " 
state  in  paying  quantities.  Certain  elements,  of  which 
oxygen,  sulphur,  and  carbon  are  the  most  important,  are 
known  as  mineralising  agents,  that  is,  they  have  combined 
with  the  metals  to  form  the  compounds  which  are  present 
in  the  ores.  But  it  is  rarely  that  these  compounds  are 
found  in  the  pure  state  ;  they  are  associated  with  more  or 
less  mechanically  mixed  earthy  matter  which  forms  the 
"gangue,"  or  "vein  stuff"  of  the  ore.  So  that  an  iron 
ore  may  be  denned  as  a  compound  of  iron  and  oxygen,  or 
of  iron,  oxygen  and  carbon,  associated  with  earthy  matter 
or  gangue.  Oxide  of  iron,  which  is  widely  distributed 
through  the  earth's  crust,  is  often  found  in  a  highly 
concentrated  state  forming  rich  deposits  of  ore  at  various 
depths  from  the  surface,  and  sometimes  in  close  proximity 
to  seams  of  coal,  beds  of  clay,  and  deposits  of  limestone. 
Sulphides  of  iron  are  very  widely  distributed,  but  are  not 
usually  regarded  as  iron  ores,  as  they  are  very  little  used 
as  such  at  present. 

The  black  magnetic  oxide  is  of  frequent  occurrence,  but 
the  red  oxide,  either  by  itself  or  combined  with  water,  is 
the  most  important  oxide,  and  ferrous  oxide  combined 
with  carbon  dioxide  in  ferrous  carbonate  is  the  iron 
compound  present  in  a  very  important  series  of  ores.  The 
principal  gangues  are  argillaceous  (chiefly  clay),  calcareous 
(chiefly  limestone),  and  siliceous  (chiefly  silica),  but  vary 
with  different  ores.  They  are  often  so  intimately  mixed 
with  the  iron  compound  as  not  to  be  distinguished  from  it ; 
this  is  especially  so  in  the  case  of  the  clay-stones  and 
spathic  ores. 

THE  CHIEF  IRON  OEES. 

Magnetite,  Fe304,  contains  72*4  per  cent  of  iron  when 
pure  ;  but  usually  gives  from  58  to  65  per  cent,  of  the 


MATERIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  17 

metal.  It  is  a  hard,  heavy,  black  stone,  that  gives  a  black 
streak  on  unglazed  porcelain.  The  gangue  is  more  or  less 
complex,  but  usually  siliceous  in  character. 

Bed  Hematite,  Fe203,  contains  70  per  cent,  of  iron  when 
pure  ;  but  usually  gives  from  40  to  62  per  cent,  of  metal. 
The  haematites  vary  very  much  in  appearance  and  physical 
character.  They  vary  from  very  dense,  hard,  and  compact 
varieties  of  a  dark  red  colour  to  less  dense,  friable  varieties 
of  a  lighter  shade  of  red ;  but  they  all  give  a  red  streak. 
The  gangue  is  variable. 

Brown  Hematite,  Fe203.  x  H20,  where  x  H20  represents 
varying  quantities  of  water  in  the  different  varieties.  Thus, 
limonite  is  represented  by  the  formula  2Fe203,3H20,  and 
gothite  by  Fe203,H20.  The  colour  and  physical  characters 
vary  considerably,  from  brown  to  yellow,  and  dense  and 
hard,  to  light  and  friable.  The  content  of  iron  varies  very 
much. 

Carbonate  Ores,  FeO.C02.  The  pure  carbonate  contains 
48*3  per  cent,  of  iron,  but  the  ores  themselves  are  very 
variable.  They  form  a  very  important  series,  and  are  of 
widely  different  characters,  which  is  largely  due  to  the 
nature  of  the  associated  gangue.  The  purest  member  of 
the  series  is  siderite,  and  this  is  closely  followed  by  the 
spathic  ores.  These  ores  vary  in  colour  from  white  to 
yellow  and  brown,  and  the  gangue  is  usually  calcareous. 
The  clay  ironstones  carry  an  argillaceous  gangue,  are 
compact  and  stony  in  appearance,  and  vary  in  colour  from 
light  to  dark  slaty  brown.  The  blackbands,  in  which  the 
ironstone,  with  its  clay  gangue,  is  intermixed  with  thin 
bands  of  coaly  matter,  are  also  important  members  of  this 
series. 

Sulphides    of    Iron. — Iron    pyrites,    FeS2,    is    the   most 

abundant   of   the   natural    sulphides,    but   is    not   worked 

directly  for  the  iron  it  contains,  nor  will  it  be  so  worked  until 

other  ores  give  out,  on  account  of  the  difficulty  and  expense 

i.s,  c 


18  IRON  AND   STEEL. 

of  getting  rid  of  the  sulphur.  It  is  brass  yellow  in  colour, 
hard,  and  readily  reduced  to  powder. 

Occurrence  of  Iron  Ores. — Deposits  of  iron  ores  are  found 
among  all  the  rock  formations  known  to  geologists,  from 
the  oldest  to  the  most  recent.  They  occur  in  veins,  beds 
and  irregular  deposits.  How  they  were  formed  is  to  some 
extent  a  matter  of  conjecture ;  but  the  simplest  expla- 
nation of  the  formation  of  veins  is  that  water,  highly 
charged  with  iron  chloride,  FeCl3,  or  iron  bicarbonate, 
Fe0.2C02.H20,  percolated  through  fissures  in  the  rocks 
already  filled  with  limestone,  and  gradually  dissolved  the 
limestone,  leaving  precipitated  oxide  of  iron  in  its  place. 
In  this  way  a  kind  of  substitution  of  one  mineral  for  another 
took  place,  the  less  soluble  rocks  forming  the  sides  of  the 
fissure  being  still  left  as  the  boundary  walls.  In  the  case 
of  magnetites  and  red  haematites  either  the  temperature  of 
the  solution  was  such  as  to  cause  the  precipitation  of  the 
anhydrous  oxide,  or  the  heat  of  the  surrounding  rocks 
was  sufficient  to  expel  the  water,  and  leave  the  ore  in  the 
anhydrous  condition.  Examples  of  such  formations  are  to 
be  found  in  the  magnetites  of  Norway  and  the  haematites 
of  Cumberland.  In  the  case  of  irregular  deposits  such  as 
those  in  the  Forest  of  Dean,  the  iron  solution  found  its  way 
into  the  limestone  beds,  dissolved  the  limestone  from  par- 
ticular portions,  and  deposited  oxide  of  iron  in  its  stead. 
In  this  way  churns  were  formed.  One  such  churn  yielded 
no  less  than  60,000  tons  of  rich  ore. 

Beds  of  ore  may  have  been  laid  down  during  the  ordi- 
nary formation  of  strata  by  the  deposition  of  oxide  of  iron 
or  carbonate  of  iron  suspended  as  fine  particles  in  the 
waters  of  lakes  and  estuaries,  or  by  the  drying  up  of  waters 
containing  the  iron  compounds  in  solution.  Or,  they  may 
have  been  formed  by  substitution  as  already  explained. 
The  ironstone  beds  associated  with  the  coal  measures  are 
good  examples. 


MATERIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  19 

The  presence  of  gangue  is  explained  on  the  assumption 
that  it  was  already  present  in  the  beds  in  which  the  sub- 
stitution took  place ;  or  that  it  was  carried  mechanically 
into  the  pores  of  the  deposited  ore  by  water  filtering 
through  it. 

Winning  the  Ore. — Mining  or  quarrying  is  resorted  to 
according  as  the  deposit  is  deep  down  in  the  earth,  or  near 
to  the  surface.  The  cost  of  deep  mining  is  heavy,  and  only 
rich  deposits  pay  for  working ;  but  quarrying  is  a  com- 
paratively inexpensive  method,  and  poorer  ones  can  be 
worked  at  a  profit.  An  excellent  example  of  iron  ore  quarry- 
ing is  to  be  found  in  the  Spanish,  province  of  Vizcaya,  which 
has  an  annual  output  of  upwards  of  four  million  tons  of 
good  haematite  ore.  The  quarrying  of  spathic  ore  from 
the  sides  of  the  Eisenberg  in  Styria  is  also  a  notable 
example.  Large  deposits  of  a  somewhat  poor  and  phos- 
phoric ore  are  now  being  quarried  in  the  neighbourhood  of 
Banbury,  Oxon.  Here  the  overburden,  as  the  overlying 
strata  are  called,  is  stripped  off,  and  put  back  again  after 
the  ore  has  been  taken  out.  The  surface  is  thus  restored 
at  a  lower  level,  and  the  value  of  the  land  but  slightly  depre- 
ciated. This  is  an  excellent  example  of  modern  method. 

Great  Britain. — The  British  Isles  have  been  and  are  still 
a  prolific  source  of  iron  ores.  All  the  ores  enumerated, 
with  perhaps  the  exception  of  magnetite,  occur  in  abun- 
dance. Magnetite  is  found  in  Devonshire  and  Yorkshire ; 
red  haematite  in  Cumberland,  Westmorland,  and  Yorkshire  ; 
brown  haematite  in  Northamptonshire,  Lincolnshire, 
Leicestershire,  Oxfordshire,  Gloucestershire,  and  Glamor- 
ganshire ;  clay  ironstones  of  the  coal  measures  in  Stafford- 
shire, Shropshire,  Derbyshire,  Warwickshire,  Yorkshire, 
and  in  Wales  and  Scotland. 

Iron  ore  is  also  found  in  Ireland,  but  it  does  not  yield  a 
large  percentage  of  iron,  and  usually  contains  a  considerable 
quantity  of  alumina ;  it  forms  a  useful  fiux. 


20  IEON  AND   STEEL. 

Germany  also  furnishes  important  deposits  of  spathic 
ores  and  haematites. 

Styria  possesses  large  deposits  of  spathic  ores. 

France  is  rich  in  ironstone  of  the  Lias  formation  in  tlie 
neighbourhood  of  Nancy;  red  haematite,  and  ironstone  of  the 
coal  measures  in  the  great  coal  centres  are  also  abundant. 

Belgium  has  large  deposits  of  ironstone  of  the  coal 
measures. 

Sweden  is  celebrated  for  its  magnetites  and  red  haema- 
tites. The  important  deposits  of  magnetite  are  at  Danne- 
mora  and  Gellivare. 

Spain  is  at  present  an  abundant  source  of  red  haematites, 
ruby  ore  and  Bilbao  ore  are  largely  exported  to  England. 

India  possesses  very  extensive  deposits  of  magnetite.  Eed 
and  brown  haematites,  and  sometimes  specular  ore,  are  found 
in  the  hill  districts,  and  are  at  present  only  superficially 
worked  by  the  natives.  They  await  future  European 
enterprise. 

America. — The  principal  ores  of  the  United  States  are 
magnetites  and  haematites,  some  of  which  are  very  rich  in 
iron.  Poor  ores  are  also  abundant,  and  when  they  con- 
tain the  magnetic  oxide  they  are  concentrated  by  magnetic 
separation. 

Canada  is  very  rich  in  deposits  of  magnetites  and 
haematites. 

Australasia  possesses  abundant  supplies  of  all  kinds  of 
ores,  which,  however,  have  not  been  worked  to  any 
extent. 

Iron  ores  are  sometimes  classified  into  non-phosphoric 
and  phosphoric  ores,  according  to  the  percentage  of  phos- 
phorus they  contain.  This  is  important,  as  in  some  of  the 
processes  of  manufacture  practically  all  the  phosphorus 
present  in  the  ore  passes  into  the  metal  separated 
from  it. 

Non-phosphoric  or£s  are  those  from  which  the  pig-iron 


MATERIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  21 

extracted  contains  less  than  0*1  per  cent,  of  phosphorus. 
They  are  principally  the  rich  magnetites  and  red  haematites 
of  Cumberland,  the  Forest  of  Dean,  Spain,  Sweden, 
America,  etc. 

Phosphoric  ores  give  pig-iron  containing  from  O'l  to 
upwards  of  2  per  cent,  of  phosphorus.  These  are  for  the 
most  part  the  clay  iron-stones  and  brown  haematites  of 
this  and  other  countries. 

The  nature  of  the  compounds  usually  present  in  iron 
ores  is  shown  in  the  Table  below. 


AVERAGE  COMPOSITION  OF  IRON  ORES. 


Compounds  Present. 

.Magnetite. 

Red 

IfaMiiatite. 

Brown 
Hicinatitc. 

Carbonates. 

rric  Oxide,  Fe20;! 

79-92 

(59-92 

ignetic  ,,      Fe8O4 

8o-41 

rrous    ,,     FeO    . 

48-13 

ica,  SiO,      .... 

5-82 

8-8(5 

9-00 

0-73 

uiniua,  AL2OS 

1-57 

1-64 

3-1(5 

4-52 

me,  CaO       .... 

1-42 

1-85 

2-93 

2-47 

ignesia,  MgO 

1-20 

0-38 

0-45 

2-36 

mganous  Oxide,  MnO 

0-56 

0-37 

0-30 

2  27 

osphoric       ,,        P2O3  . 

0-11 

0-02 

0-90 

0-53 

Iphur,  S       . 

0-04 

()"()! 

0-01 

rbon  Dioxide,  C02 

32-28 

ater,  H2O     .... 

0-72 

6-95 

13-34 

1-70 

soluble  Matter 

3-15 

100-00 

100-00 

100-00 

100-00 

FUEL. 

Materials  used  for  the  generation  of  heat  on  the  large 
scale  are  required  in  enormous  quantities  in  the  manu- 
facture of  iron  and  steel,  and  a  plentiful  and  cheap  supply 
at  the  works  is  one  of  the  essentials  to  their  success.  Coal 
is  the  most  important  of  these  heat  generators,  and  a  short 


22  IEON  AND  STEEL. 

account  of  its  origin,  nature  and  distribution  will  be  useful 
in  following  out  its  application. 

Coal  has  been  defined  as  mineralised  vegetable  matter, 
and  occurs  for  the  most  part  in  beds  or  seams  among  the 
rock  formations  of  the  carboniferous  system,  which  is 
bounded  by  the  old  red  sandstone  below  and  the  new  red 
sandstone  above.  This  system,  which  is  without  doubt  the 
most  important  to  the  iron  industry,  contains  beds  of  lime- 
stone, clay,  and  ironstone,  in  addition  to  the  coal  measures, 
and  indicates  the  existence  of  prolific  vegetable  life  and  of 
the  lower  forms  of  animal  life  on  the  earth's  surface  during 
its  formation.  Dense  masses  of  vegetation  must  have 
accumulated  at  the  estuaries  of  enormous  rivers,  to  be 
submerged,  then  to  be  covered  by  rock-forming  materials 
during  periodic  inundations,  and  to  undergo  that  slow 
decay  out  of  contact  with  air  that  has  resulted  in  the  con- 
centration of  carbon  in  the  enormous  masses  of  coal  which 
form  part  of  the  system.  Sometimes  the  coal  beds  crop 
out  near  the  surface,  but  generally  shafts  have  to  be  sunk 
through  the  overlying  strata  to  reach  them. 

The  elemental  constituents  of  vegetable  matter  are 
carbon,  hydrogen,  oxygen,  and  nitrogen ;  and  in  addition 
there  is  inorganic  matter  which  is  left  behind  as  ash  when 
the  substance  is  completely  burned.  During  its  conversion 
into  coal  gaseous  matter  is  liberated,  and  carbon  becomes 
concentrated  in  a  smaller  mass  of  material.  The  thermal 
value  of  the  coal  depends  largely  upon  this  concentration 
of  carbon,  and  the  composition  of  the  different  varieties 
brings  this  out  very  clearly.  The  older  the  deposit  the 
more  pronounced  is  the  change,  and  the  nearer  the  coal 
approaches  in  composition  to  pure  carbon. 

Coals  are  usually  classified  into  three  groups :  (1) 
Lignites,  (2)  Coals,  (3)  Anthracites,-  but  there  is  no  very 
sharp  line  between  them.  Some  coals  give  out  a  large 
quantity  of  combustible  gas  when  strongly  heated  out  of 


MATERIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  23 

contact  with  air ;  others  give  out  a  much  smaller  quantity 
under  the  same  conditions.  This  gives  rise  to  the  classifi- 
cation into  long  flaming  and  short  flaming  coals.  Some 
varieties  also  leave  a  firmly  coherent  residue  after  all  the 
gaseous  matter  has  been  driven  out  of  the  powdered  coal  ; 
others  leave  a  pulverulent  residue.  The  former  are  the 
caking  coals,  and  the  latter  the  non-caking  coals,  or  free- 
burning  coals. 

Lignites  are  coals  belonging  to  more  recent  formations 
than  the  carboniferous  system,  and  still  show  traces  of 
their  woody  (ligneous)  origin.  They  vary  very  much  in 
appearance,  from'  brown,  dull  and  earthy,  to  black  and 
shining ;  but  they  all  give  off  a  dense  black  smoke  when 
burnt  in  a  moderate  current  of  air.  When  lignites  are 
strongly  heated  out  of  contact  with  air,  much  water  and 
volatile  matter  is  driven  off,  and  a  residue  of  less  than 
50  per  cent,  of  friable  coke  is  obtained.  The  total  carbon 
varies  from  57  to  75  per  cent.,  and  the  ash  from  3  to  30 
per  cent.  The  principal  drawback  to  the  use  of  lignites 
as  fuel  is  the  large  amount  of  water  they  contain,  which 
in  the  freshly-mined  fuel  may  reach  30  per  cent.,  but  about 
half  of  it  disappears  on  air  drying.  Lignites  are  found  in 
parts  of  Germany. 

Coals  belonging  to  the  carboniferous  age  have  a  deep 
black  colour,  shiny  appearance,  and  lamellar  fracture.  In 
them  the  ligneous  structure  has  entirely  disappeared. 
They  vary  much  in  properties  and  composition  ;  and  even 
those  of  the  same  composition  may  vary  widely  according  to 
the  manner  in  which  their  elements  are  combined  together. 
The  amount  of  fixed  carbon  is  always  greater  than  50  per 
cent.,  and  from  a  good  coking  coal  upwards  of  80  per  cent, 
may  be  obtained.  The  total  carbon  varies  from  75  to  93 
per  cent.,  and  the  ash  from  1  to  30  per  cent.,  but  rarely 
exceeds  8  per  cent.  The  volatile  matter  varies  between  43 
and  15  per  cent.  Free  burning  and  long  flaming  coals  are 


24  IRON  AND   STEEL. 

the  best  for  furnace  work ;  the  short  flaming  coals  are 
most  suitable  for  conversion  into  coke.  The  Welsh  steam 
coal  is  a  good  example  of  a  free-burning  coal  used  for  the 
firing  of  marine  and  locomotive  boilers.  They  are  found 
in  all  the  coal-bearing  districts  of  the  world. 

Anthracites. — These  are  the  most  concentrated  form  of  coal. 
They  contain  from  93  to  95  per  cent,  of  carbon,  and  leave 
a  residue  of  coke  from  85  to  93  per  cent.,  which,  however, 
shows  no  indication  of  caking  even  at  a  bright  red  heat. 
They  are  bright  jet  black  in  colour,  homogeneous  in 
structure,  and  clean  to  handle.  The  moisture  is  small, 
and  the  ash  varies  from  1  to  6  per  cent.  The  South  Wales 
and  Pennsylvanian  deposits  are  the  most  noted. 

Testing  Coal. — Much  information  of  the  general  character 
of  a  sample  of  coal  may  be  obtained  from  the  following 
simple  experiments  :— 

(1)  The  sample  of  coal  to  be  tested  is  crushed  to  a  coarse 
powder,  400  grains  weighed  into  a  small  clay  crucible,  and 
the  lid  carefully  luted  on  with  moist  clay,  a  small  space 
being  left  for  the  escape  of  gas.     The  crucible  is  then  heated 
to  a  bright  red  heat  for  twenty  minutes,  and  the  general 
appearance  of  the  flame  of  the  escaping  gas  noted.    When 
the  crucible  is  cold  the  lid  is  removed,  the  residue  weighed 
and  examined.     A  simple  calculation  gives  the  percentage 
of  coke,  and  the  percentage  of  volatile  matter  is  obtained  by 
difference. 

(2)  Fifty  grains  of  the  finely-powdered  coal  are  weighed 
in  a  porcelain  crucible,  and  heated  in  a  muffle  furnace  at  a 
bright  red  heat.     When  the  coal  is  completely  burnt  the 
residue  of  ash  is  weighed,  and  the  weight  multiplied  by  2 
gives  the  percentage. 

Calorific  Power. — To  obtain  fuller  information  it  is 
necessary  to  determine  the  elemental  composition  of  the 
coal  by  actual  analysis.  In  computing  the  heat-giving 
power  of  the  fuel  frpui  its  composition  it  is  usual  to 


MATERIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  25 


consider  the    whole  of   the  carbon  as    available    for    the 
generation  of  heat,  but  only  that  portion  of  the  hydrogen 
in    excess    of   the   amount   required  to  combine  with  the 
whole  of  the  oxygen   present   in   the  coal  to  form  water. 
This    excess,    or    available    hydrogen,  as  it  is  called,  and 
the  whole  of  the  carbon,  are  the  useful  combustible  con- 
stituents of  the  coal,  and  when  their  percentages  are  known 
the  calorific  power  of  the  fuel  can  be  calculated.    Carbon 
develops  its  maximum  amount  of  heat  when  it  burns  to 
form  carbon  dioxide,  and  one  pound  of  charcoal  gives  out 
sufficient  heat  to  raise  8,080  pounds  of  water 
through  1°  C.,  and  this  is  the  measure  of  the 
calorific  power  of  carbon.    Similarly,  one  pound 
of   hydrogen  when    burnt  to  water  furnishes 
sufficient  heat  to  raise  34,462  pounds  of  water 
through  1°  C.     The  unit  quantity  of  heat  may 
be  taken  as  that  quantity  required  to  raise  one 
pound  of  water  through  1°  C.  in  temperature. 
A  steam  unit  is  also  used  in  which  the  heat  re- 
quired to  convert  one  pound  of  water  at  100°  C. 
into  steam  at  the  same  temperature  is  taken. 
It  is  537   times  greater  than  the  water  unit. 
But  what  the  practical  man  wants  is  a  quick, 
ready  method  of  determining  the  calorific  power  of  a  fuel, 
and  though  the  result  may  be  only  approximate  it  is  usually 
sufficiently  close  for  his  purpose.     The  Thompson  calori- 
meter is  largely  used  in  comparing  the  calorific  values  of 
various  coals.      A  weighed  quantity  of  the  finely-powdered 
and  dried  coal  is  mixed  with  sufficient  saltpetre  and  chlorate 
of  potash  to  furnish   the   oxygen   for   its   complete   com- 
bustion.    The  mixture  is  then  packed  in  a  metal  cylinder 
and  a  short  cotton  fuse  pushed  into  it  ready  for  firing. 
The   cylinder   is   held   on   a   perforated    stand    by    metal 
springs,  and  when  the  fuse  is  ignited  a  metal  chamber, 
open  at  the  bottom,  is  pushed  over  the  springs,  and  the 


FIG.  l. 


26  IRON  AND  STEEL. 

whole  is  immersed  in  a  glass  vessel  containing  a  weighed 
quantity  of  water  at  a  known  temperature.  The  fuse  on 
burning  down  to  the  mixture  fires  it,  and  the  gaseous 
products  of  the  combustion  are  forced  by  their  own  pressure 
through  the  holes  in  the  bottom  of  the  stand,  and  escape 
through  the  water  by  which  their  heat  is  absorbed  before 
they  pass  into  the  air.  When  the  combustion  is  finished  a 
tap  connected  with  the  chamber  is  opened,  and  the  interior 
of  the  chamber  flooded,  so  that  the  whole  of  the  heat  is 
absorbed  by  the  water.  The  temperature  of  the  water  is 
then  taken,  and  the  experiment  is  finished.  From  the 
weight  of  coal  burnt,  the  weight  of  water  in  the  vessel,  and 
its  rise  in  temperature,  the  calorific  power  of  the  fuel  can 
be  calculated.  The  apparatus  is  shown  in  Fig  1.  The  heat 
lost  owing  to  the  roughness  of  the  experiment  is  estimated 
at  10  per  cent,  of  the  whole,  and  this  is  allowed  for. 

Example  :    Weight  of  coal  30  grains. 

,,  water  29,010  grains. 

Kise  in  temperature  6*5°  C. 

Then  2901°  X  6'5  =  6285  +  628  =  6913 


That  is,  the  heat  generated  when  lib.  of  the  coal  is 
completely  burnt  would  raise  6,913  Ibs.  of  water  through 

6913 

1°  C.,  or  would  evaporate  -      r  =   12'8    Ibs.    of    water    at 

5o7 

100°  C.  to  steam  at  the  same  temperature. 

The  complete  apparatus  is  sold  for  use  in  the  works,  and 
when  the  instructions  are  followed  it  is  only  necessary  to 
read  the  temperature  in  degrees  Fahrenheit,  and  then  add 
10  per  cent,  to  at  once  obtain  the  evaporative  power  of  the 
coal  being  tested. 

In    the   case    of-  a    dense   fuel,  such    as   hard   coke   or 


MATERIALS  USED  IN  IEON  AND  STEEL  MANUFACTURE.  27 

anthracite,  it  is  often  necessary  to  mix  with  it  a  weighed 
quantity  of  a  more  easily  burnt  coal,  or  charcoal,  the  calorific 
power  of  which  is  known.  The  calorific  value  of  the  fuel 
under  examination  is  then  obtained  by  difference. 

Similar  apparatus  is  also  in  use  in  which  a  stream  of 
oxygen  gas  is  passed  through  the  combustion  chamber  to 
take  the  place  of  the  chlorate  and  saltpetre,  and  the 
products  of  combustion  are  made  to  pass  through  the  water 
in  the  calorimeter. 

For  very  accurate  determinations  a  more  elaborate  form 
of  apparatus  is  necessary,  and  the  Berthelot-Mahler 
calorimeter  is  largely  used  for  the  purpose.  It  consists  of 
a  steel  shell  which  has  been  nickel-plated  outside  and 
enamelled  inside,  and  is  fitted  with  a  screw  top  provided 
with  a  tap  through  which  a  gas  can  be  forced  into  the 
interior.  The  fuel  to  be  burnt  is  placed  in  a  platinum 
cup  suspended  from  the  under  side  of  the  movable  top,  and 
sufficient  oxygen  to  burn  it  is  forced  under  pressure  into 
the  shell.  The  bomb  is  then  completely  immersed  in  the 
water  contained  in  the  calorimeter  vessel,  which  is  very 
carefully  protected  from  loss  of  heat  by  a  surrounding 
jacket.  The  fuel  is  ignited  by  passing  an  electric  current 
through  a  spiral  of  thin  platinum  wire  suspended  just 
above  it.  The  spiral  becomes  red  hot  and  ignites  the  fuel, 
which  then  burns  vigorously  in  the  compressed  oxygen. 
The  heat  developed  is  absorbed  by  the  water  in  the 
calorimeter,  and  its  quantity  determined.  All  kinds  of 
fuel,  solid,  liquid,  and  gaseous,  can  be  burnt  in  this 
apparatus  with  very  accurate  results ;  but  many  pre- 
cautions have  to  be  taken,  and  corrections  made,  to  obtain 
them. 

The  calorific  power  of  a  combustible  body  can  also  be 
calculated  from  its  composition,  but  for  this  purpose  the 
analysis  of  the  fuel  is  required.  The  following  is  given  as 
an  example  of  this  method  :— 


28  IEON  AND   STEEL. 

A  sample  of  coal  was  found  to  contain— 

Carbon      .....       68*01  per  cent. 
Hydrogen          ....          3'33 
Oxygen     .....         5'21         „ 

Constituents  not  given  consisted  of  moisture,  ash, 
sulphur,  etc. 

Then  the  weight  of  carbon  in  unit  weight  of  the 

fuel =  0-6801 

And  the  number  of  units  of  heat  liberated  by 

its  combustion  =  0'6801  X  8080  .  .  =  5494 

The   weight   of    available   hydrogen    in    unit 

weight  of  the  fuel  =  0'0333  -  °'°Q521        .  =  0'0268 

o 

And  the  units  of   heat  liberated  by  its  com- 
bustion =  0-0268  X  34462         .      .    .         .  =        924 

Therefore  calorific  power  =  5494  +  924   .         .  =      6418 

The  number  obtained  by  an  actual  combustion 

was 6370 

The  observed  and  calculated  values  are  found  to  agree 
fairly  well  in  the  majority  of  cases,  which  gives  confidence 
in  the  practical  methods. 

The  calorific  power  of  a  fuel  may  then  be  defined  as  the 
number  of  units  of  heat  developed  by  the  complete  com- 
bustion of  a  unit  weight  of  the  fuel.  In  measuring  the  heat 
it  is  necessary  for  the  products  of  combustion  to  come  to 
the  same  temperature  as  the  materials  were  when  the  com- 
bustion commenced.  The  whole  of  the  effective  heat  is 
thus  measured.  The  unit  of  heat  is  arbitrary,  but  when 
once  fixed  is  definite.  Water  is  commonly  used  as  the 
absorbing  medium  on  account  of  its  great  capacity  for  heat, 
or  specific  heat  as  it  is  called.  It  has  the  highest  specific 
heat  of  any  pure  substance,  either  solid,  liquid,  or  gaseous, 
and  is  taken  as  unity.  All  other  substances  have,  therefore, 
specific  heats  less  than  1. 


MATERIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  29 

The  following  Table  gives  the  calorific  power  of  a  number 
of  common  bodies.  The  unit  weight  may  be  taken  as 
1  Ib.  and  the  unit  temperature  as  1°  C. 

TABLE  OF  CALORIFIC  POWER. 


Substance  burnt. 

Compounds 
Formed. 

Units  of  Heat. 

Charcoal,   C  . 

CO2 

8080 

Graphite,  C  . 

C02 

7797 

I  Hamond    C 

no 

777O 

Carbon,  C      ...... 

\J  \J*> 

CO 

i  I  1  U 

2473 

Marsh  Gas,  CH4    .                   ... 

CO,;  H,0 

13063 

Olefiant  Gas,  C2H4 

CO,;  ILO 

11857 

Carbon  Monoxide,  CO          ... 

C02 

2400 

Hydrogen,  H2       ..... 

HoO 

34462 

Silicon,  Si     

SiO, 

7830 

Phosphorus,  P      

P20S 

5700 

Iron,  Fe        ...... 

1181 

Dry  Wood    

CO2;''HoO 

3616 

Coal,  average        ..... 

C02;  H2O 

8000 

Coke,  average       

COa 

7000 

Anthracite    ...... 

C02 

8460 

Sulphur,  S    .                            ... 

S02 

2240 

Note.  —  Carbon  monoxide  contains  7                "   =   _  of  its 

CO         28         1 

weight  of  carbon,  so  that  unit  weight  of  carbon  is  contained 

7  7 

in  '-  of  the  oxide.     Therefore  2400  X  7:  =  5600  heat  units 
o  d 

are  obtained  by  burning  the  weight  of  carbon  monoxide  con- 
taining unit  weight  of  carbon.  Then  2473  +  5600  =  8073. 
Thus  it  is  evident  that  the  same  quantity  of  heat  is 
developed  whether  the  carbon  is  burnt  in  two  stages,  or 
at  once.  This  is  generally  true  for  other  combustible 
bodies  that  admit  of  partial  as  well  as  complete  combustion. 
Calorific  Intensity. — This  term  indicates  the  temperature 
to  which  the  products  of  a  given  combustion  would  be 
raised  if  the  whole  of  the  heat  developed  were  confined  to 


30  IRON  AND   STEEL. 

these  products.  This  is,  however,  never  the  case,  so  that 
the  practical  temperature  always  falls  short,  and  often  very 
short,  of  the  theoretical  one  ;  but  the  more  rapid  the  action 
the  higher  the  temperature  obtained,  for  there  is  less  time 
for  the  heat  to  escape  into  surrounding  bodies. 

The  quantities  to  be  taken  into  account  in  calculating 
the  calorific  intensity  of  a  given  fuel  are  :  (i.)  the  weight  of 
the  fuel ;  (ii.)  its  calorific  power ;  (iii.)  the  weight  of  the 
products  of  combustion  ;  (iv.)  their  specific  heats.  Also,  if 
there  is  any  inert  matter  within  the  zone  of  combustion, 
that  too  has  to  be  raised  to  the  same  temperature,  so  that 
its  weight  and  specific  heat  must  also  be  taken  into  account. 
The  usual  plan  is  to  take  unit  weight  of  the  fuel,  which 
simplifies  the  general  statement.  Thus — 


Calorific  pcrwer  of  fuel 


Weight  of  products  of  combustion  x  Specific  heat  of  products 


=  Calorific  intensity. 


The  following  examples  will  serve  to  illustrate  the  general 
principles  :— 

(1)  Carbon  burning  in  oxygen.  The  product  of  com- 
bustion is  carbon  dioxide,  C02.  Now  the  proportion  of 

OO  Q 

oxygen  to  carbon  in  this  compound  is  —  =  -;    therefore 

\.2i        o 

the  weight  of  the  product  containing  unit  weight  of  carbon 

,3-=  3'66,  and  the  specific  heat  of  carbon  dioxide  is 
o 

0-2164. 


(2)  Carbon  burning  in  air.  Here  the  inert  nitrogen  in 
the  air  is  mixed  with  the  products,  and  must  be  raised  to 
the  same  temperature.  The  proportion  between  the 
weights  of  oxygen  and  nitrogen  to  the  air  is  1  :  3'35. 
Therefore  the  2'66  parts  of  oxygen  will  bring  2'66  X  3*35 
F=  8'  9  parts  of  nitrogen  into  the  combustion  zone.  The 


MATERIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  ;J1 

specific   heat   of    nitrogen   is   0'244,   and    the    statement 
becomes— 

8080 

8-66  X  0-2164  +  8-9  X  0-244  "  2727°  c- 
This  brings  out  clearly  the  great  influence  of  inert  matter 
in  the  combustion  zone  upon  its  temperature. 

Sntyhur  is  invariably  present  in  coal,  usually  as  iron 
pyrites,  FeS,,  and  sulphate  of  lime,  CaS04.  It  is  very 
objectionable  in  some  processes,  and  is  very  difficult  to 
remove  completely.  Fuels  used  for  particular  purposes 
are  analysed  to  determine 
the  percentage  of  sulphur 
present  in  them. 

Charcoal.  —  -  This  fuel  is 
used  to  some  extent  in  the 
metallurgy  of  iron,  and  is  pre- 
pared by  heating  sound,  well 
grown  wood  in  contact  with  a  FIG.  2.— Charcoal  Pile, 

limited  supply  of    air.      The 

usual  plan  is  to  make  the  logs  into  a  circular  pile  round  a 
rough  wooden  chimney,  and  cover  it  with  turf  and  soil  so 
as  to  make  it  fairly  airtight.  The  pile  is  then  fired  from 
the  top  of  the  chimney,  and  the  "  burning  "  regulated  by 
making  holes  in  the  cover.  The  combustible  gas  driven 
out  of  the  wood  by  the  heat  burns  within  the  pile  and 
carries  on  the  charring.  When  the  pile  is  "  burnt  "  out 
the  cover  is  removed,  and  the  hot  charcoal  quenched  with 
water.  The  general  arrangement  of  the  pile  is  shown  in 
Fig.  2.  The  average  yield  is  about  20  per  cent,  by  weight 
of  the  original  wood,  and  the  average  composition  of  the 
charcoal  free  from  ash  is,  carbon  =  90  per  cent.,  hydrogen 
=  3  per  cent.,  oxygen  and  nitrogen  —  7  per  cent.  Thus 
there  is  about  10  per  cent,  of  gaseous  matter  left  in  the 
product.  Charcoal  is  usually  free  from  sulphur,  and  the 
ash  amounts  to  about  1  per  cent. 


32  IEON  AND   STEEL. 

Coke. — This  is  the  most  important  prepared  fuel,  and  is 
made  in  large  quantities.  Coke  of  good,  or  even  of  medium 
quality,  is  a  hard,  compact,  coherent  body.  It  is  grey  in 
colour,  and  usually  has  a  more  or  less  columnar  structure. 
It  contains  the  fixed  carbon,  a  little  oxygen  and  hydrogen, 
the  whole  of  the  ash,  and  the  greater  part  of  the  sulphur 
originally  present  in  the  coal  from  which  it  was  manu- 
factured. Omitting  the  gaseous  constituents,  an  average 
coke  for  blast  furnace  work  should  be  sufficiently  hard  and 
compact  to  bear  the  furnace  burden  without  breaking  down, 
and  should  have  the  following  composition  :— 

Average  Composition  of  Coke. 

Carbon 90 

Ash 7 

Sulphur         .         .         .         .         .         .         .1 

Moisture  2 


100 

In  modern  coke  manufacture  the  primary  object  is  to 
obtain  the  maximum  quantity  of  suitable  coke  from  the 
coal  used,  arid  to  utilise  as  far  as  possible  the  useful  con- 
stituents of  the  volatile  matter  driven  out  of  the  coal  during 
the  coking  operation.  To  obtain  the  maximum  yield  the 
coking  must  be  conducted  in  a  chamber  from  which  the  air 
is  excluded,  and  the  old  wasteful  methods  of  coking  in  piles, 
kilns,  and  ovens  into  the  interior  of  which  air  must  be 
admitted  to  carry  on  the  coking,  are  gradually  giving  way 
to  the  more  scientific  methods  of  modern  practice.  The 
first  principle  of  coking  is  that  the  combustible  volatile 
matter  shall  furnish  the  heat  necessary  to  carry  on  the 
operation,  and  that  this  is  more  than  sufficient  will  appear 
in  the  sequel.  If  it  is  to  be  burnt  in  the  coking  space  then 
air  must  be  admitted  to  burn  it,  and  it  is  impossible  to  so 


MATEEIALS  USED  IN  IKON  AND  STEEL  MANUFACTURE.  33 

regulate  the  admission  of  air  that  none  of  the  fixed  carbon 
shall  be  burnt.  Hence  such  a  method  must  be  wasteful. 
But  there  is  no  difficulty  in  burning  the  gases  outside  the 
coking  chamber  while  still  using  the  heat  for  coking,  and 
so  doing  away  with  the  necessity  of  admitting  air  into  the 
chamber.  A  large  number  of  coke  ovens  are  based  upon 
this  principle,  but  a  brief  description  of  one  of  the  most 
modern  will  suffice  to  make  the  method  clear. 

The  Otto-Hoffman  Coke  Oven. — The  coking  chamber  in 
this  oven  is  rectangular  in  section,  and  is  closed  at  both 
ends  by  tightly  fitting  doors,  so  as  to  exclude  the  air  as 
completely  as  possible.  The  internal  dimensions  of  the 
chamber  are  about  30  feet  long,  2  feet  wide,  and  4  feet 
high.  The  walls  are  constructed  of  fire-brick,  and  have  a 
number  of  vertical  flues  running  through  them  which  are 
connected  with  horizontal  flues  under  the  floor  of  the 
chamber.  Along  the  top  are  three  holes  at  regular 
intervals  through  which  the  crushed  coal  is  charged. 
These  are  made  air-tight  while  the  coking  is  going  on. 
Between  these  are  two  vertical  pipes  connected  with 
horizontal  pipes  through  which  the  volatile  matter  is  drawn 
off  from  the  chamber  as  fast  as  it  is  liberated  from  the  coal. 
Below  the  floor  level  at  each  end  of  the  coking  chamber 
and  in  the  foundation  are  two  rectangular  chambers  lined 
with  fire-bricks,  and  partly  filled  with  a  chequer  work  of 
fire-brick.  These  are  the  regenerators,  and  just  above  them 
are  the  mains  for  bringing  back  the  combustible  gas  to  the 
oven.  The  oven  works  continuously,  and  the  walls  of  the 
chambers  are  always  hot,  so  that  directly  a  charge  is  intro- 
duced the  coking  commences.  The  volatile  matter  is  drawn 
off  through  the  mains  to  condensers  and  scrubbers  by 
which  the  watery  liquid  containing  ammonium  compounds 
and  the  tar  are  separated.  The  gas  then  passes  back  to 
the  oven,  and  enters  a  wide  flue  under  the  bottom  of  the 
chamber,  where  it  mixes  with  hot  air  driven  in  through 


34 


IRON  AND   STEEL. 


the  regenerator  at  that  end  by  a  fan.  The  flame  and 
products  of  combustion  from  this  burning  gas  then  pass  up 
the  vertical  flues  in  one  wall  over  the  top  of  the  chamber 
and  down  through  corresponding  vertical  flues  in  the  other 
wall  into  another  horizontal  flue,  from  which  they  pass  into 
the  regenerator  at  the  other  end  of  the  chamber,  where  they 
leave  the  greater  part  of  their  waste  heat  before  escaping 
into  an  underground  flue.  Thus  practically  the  whole  of 


PIG.  3.— The  Otto-Hoffman  Coke  Oven. 

A.  Charging  holes.  D.  Gas  mains,  intake. 

B.  Coking  chamber.  E.  Eegenerators. 

C.  Gas  mains,  outtake.  F.  Vertical  flues. 

the  heat  developed  by  the  burning  gas  is  kept  in  the  oven 
to  carry  on  the  coking.  When  the  regenerator  has  cooled 
down  somewhat,  due  to  the  loss  of  the  heat  carried  back 
into  the  oven  by  the  air  passing  through  it,  the  order  of 
working  is  changed.  The  gas  is  cut  off  from  the  one  end 
and  turned  on  at  the  other,  and  the  air  is  forced  through 
the  second  regenerator,  which  has  now  been  heated  up  by 
the  waste  heat.  The  course  of  the  products  of  combustion 
is  now  just  exactly  the  opposite  of  what  it  was  before,  and 
the  cooled  regenerator  absorbs  heat  from  the  escaping 


MATERIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  35 

gases.  This  reversal  takes  place  periodically,  and  is  readily 
effected  by  an  arrangement  of  valves  connected  with  the 
air  and  gas  passages.  Several  of  these  chambers  are 
built  in  one  block,  and  worked  together.  A  block  of  sixty, 
with  the  necessary  condensing  plant,  costs  about  ^36,000 
to  construct. 

When  the  coking  is  finished  both  doors  are  opened,  a 
power  ram  is  brought  into  contact  with  the  mass  of  coke  at 
one  end,  and  it  is  pushed  out  bodily  at  the  other.  As  it 
leaves  the  chamber  water  is  squirted  on  it  to  prevent  waste 
by  oxidation.  The  empty  chamber  is  re-charged  at  once, 
and  the  working  continues.  The  doors  are  generally  in  two 
parts,  so  that  the  bottom  portions  may  be  closed  and  the 
top  left  open  for  spreading  the  incoming  charge.  See  Fig.  3. 

The  salving  of  the  tar  and  ammoniacal  liquor  consider- 
ably reduces  the  cost  of  coking,  and  pays  for  the  erection  of 
costly  condensing  apparatus  on  account  of  the  value  of  these 
by-products.  With  a  good  coking  coal  the  yield  of  coke 
amounts  to  75  per  cent,  of  the  coal  used.  The  coal  is 
crushed,  and  often  washed  when  it  is  desired  to  get  rid  of 
pyritic  and  earthy  matter  so  as  to  reduce  the  percentage  of 
ash  and  sulphur  as  much  as  possible.  Some  sulphur  is 
removed  during  coking  and  quenching,  but  not  all.  So 
that  coke  always  contains  sulphur.  The  coke  produced  in 
these  ovens  is  good,  coherent  material,  and  suitable  for 
blast  furnace  work. 

Gaseous  Fuel. — The  primitive  process  of  burning  solid 
fuel  in  an  open  grate,  although  very  wasteful,  still  persists 
to  a  considerable  extent ;  but  the  use  of  gaseous  fuel  for  all 
purposes  is  increasing,  and  is  a  distinct  advance  both  from 
the  economical  and  hygienic  point  of  view.  As  already 
pointed  out,  ordinary  coal  contains  a  considerable  proportion 
of  combustible  volatile  matter,  which  is  driven  out  of  the 
coal  by  heat  alone,  but  it  is  also  possible  to  convert  nearly 
all  the  fixed  carbon  into  combustible  gas,  and  thus  obtain 

D  2 


36  IRON  AND   STEEL. 

practically  the  whole  of  the  heat-producing  portion  of  the 
coal  in  the  gaseous  form.  This  is  made  clear  by  consider- 
ing the  chemical  changes  that  take  place  in  an  open  fire, 
and  the  way  in  which  they  can  be  modified.  When  a  fresh 
supply  of  coal  is  thrown  into  the  grate  the  heat  from  the 
burning  of  the  fuel  already  there  expels  the  volatile  matter 
from  the  fresh  fuel  with  the  production  of  smoke  and  flame. 
A  current  of  air  entering  the  bottom  of  the  grate  passes 
through  the  fire  and  supplies  the  necessary  oxygen  to  carry 
on  the  combustion  of  the  carbon,  upon  which  the  develop- 
ment of  heat  depends.  In  the  complete  burning  of  the 
coke  carbon  dioxide  is  formed,  thus : 

C  +  02  =  C02. 

Now  the  whole  of  the  oxygen  is  used  up  before  the  current 
of  air  reaches  the  top  of  the  fire,  and  the  deeper  the  layer 
of  fuel  the  further  the  gases  will  have  to  travel  before 
escaping  from  the  top.  The  oxygen  of  the  air  is  replaced 
by  carbon  dioxide,  and  this  gas  coming  into  contact  with 
red-hot  carbon  loses  part  of  its  oxygen,  and  the  combustible 
gas,  carbon  monoxide,  is  formed  thus  : 

C  +  C02  -  2  CO. 

This  gas  burns  with  a  blue  flame  over  the  top  of  the  fire. 
The  combustion  taking  place  there  is  due  to  the  current  of 
air  passing  over  the  fire  on  its  way  to  the  chimney.  Also, 
the  water  vapour,  which  is  always  present  in  the  air  passing 
into  the  fire,  undergoes  changes  by  which  carbon  monoxide, 
hydrogen,  and  marsh  gas  are  formed  thus  : 

(1)  C  +  H20  =  CO  +  H2. 

(2)  3  C  +  2  H20  -  2  CO  +  CH4 

The  change  represented  in  (2)  takes  place  to  a  much  smaller 
extent  that  represented  by  (1).  Now  the  reactions  by  which 
carbon  monoxide  alone  is  formed  are  exothermic,  or  heat 
producing,  but  those  in  which  water  is  decomposed  by 


MATERIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  37 

carbon  are  cndothermic,  or  heat  absorbing,  and  unless 
sufficient  heat  is  developed  by  the  other  reactions  to  keep 
the  carbon  above  a  limiting  temperature,  the  decomposition 
of  water  vapour  ceases. 

It  is  clear  that  if  the  upper  current  of  air  is  entirely  cut 
off  by  closing  the  top  of  the  grate,  the  combustible  gas 
formed  by  the  coking,  together  with  that  formed  in  the 
interior  of  the  fire,  must  pass  up  the  flue  unburnt,  and 
could  be  drawn  off  to  be  burnt  in  any  convenient  place. 
Combustible  gaseous  matter  obtained  in  this  way  is  known 
as  "  producer  gas,"  and  in  making  it  the  aim  should  be  to 
so  regulate  the  proportions  of  air  and  water  vapour  as  to 
get  as  large  a  proportion  of  carbon  monoxide  and  hydrogen, 
and  as  small  a  proportion  of  carbon  dioxide  as  possible. 
It  seems,  however,  that  a  certain  proportion  of  this  gas 
must  be  formed  in  order  to  keep  up  the  necessary 
temperature. 

As  the  nitrogen  of  the  air  cannot  be  excluded,  this  gas 
is  always  present  in  large  quantity.  An  average  composi- 
tion for  producer  gas  may  be  given  as  follows,  but  this  may 
vary  considerably  with  the  kind  of  apparatus  used,  and  with 
the  mode  of  working  it : 

Nitrogen,  N2          .         .  55  \  Non- combustible, 

,  Carbon  Dioxide,  C02     .     5  j  60% 

Producer    )  Carbon  Monoxid6)  co  .  25  \ 

Hydrogen,  H2        .         .10     Combustible,  40% 
^  Hydrocarbons        .         .     5  J 

It  is  well  known  that  a  large  excess  of  steam  maybe  used 
under  proper  conditions,  but  in  that  case  more  of  the 
carbon  is  converted  into  carbon  dioxide.  This  is  shown  by 
the  equation : 

C  +  2  H20  =  CO,  +  2  H2. 


38  IKON    AND   STEEL. 

And  this  is  the  chief  reaction  used  in  the  production  of 
"  Mond  gas,"  which  contains  : 

Nitrogen,  N2        .         .43]  Non -combustible, 
Carbon  Dioxide,  C02    .  17  J  60% 

Mond  Gas  -\  Carbon  Monoxide,  CO    11 


Hydrogen,  H2      .         .27 
Hydrocarbons      .         .     2 


Combustible,  40% 


As  this  gas  contains  a  smaller  proportion  of  the  poisonous 
carbon  monoxide,  it  is  much  safer  to  use  by  the  inex- 
perienced or  careless,  and  will  no  doubt  be  largely  used  in 
the  future. 

On  the  other  hand,  when  steam  is  blown  through  very  hot 
coke,  the  issuing  gas  is  almost  entirely  a  mixture  of 
carbon  monoxide  and  hydrogen,  and  is  known  as  "  water 
gas."  But  the  production  of  this  gas  is  intermittent,  for 
the  reaction  is  endothermic,  and  the  coke  cools  rapidly  under 
the  action  of  the  steam.  This  difficulty  is  got  over  by 
cutting  off  the  steam,  and  blowing  air  through  at  intervals 
to  heat  up  the  coke. 

Nitrogen,  N2        .         .     3  )  Non  -combustible, 
Carbon  Dioxide,  C02   .     4  J  7% 


Water  Gas 


Carbon  Monoxide,  CO    52 
Hydrogen,  H2  .41 


^  |  Combustible,  93% 


There  are  numerous  forms  of  producer,  as  the  apparatus 
is  called,  all  of  which  have  points  in  their  favour  ;  but  the 
names  of  Siemens  and  Wilson  will  always  stand  out  in 
connection  with  the  pioneer  work  in  the  use  of  gaseous 
fuel.  It  will,  however,  be  better  to  describe  one  of  the 
more  recent  forms  of  producers  in  order  to  make  clear 
the  general  principles  as  they  are  applied  now. 

One  of  the  principal  difficulties  in  the  working  of  a  pro- 
ducer plant  which  is  not  constructed  to  salve  the  by- 
products is  caused  by  the  accumulation  of  tar  in  the 


MATEEIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  ;39 

gas  mains.  This  not  only  makes  the  working  less  satisfac- 
tory, but  also  causes  waste  of  combustible  matter,  and 
recent  developments  have  been  in  the  direction  of  preventing 
this  waste.  Another  difficulty  met  with  in  the  early  working 
was  the  removal  of  the  ashes,  and  in  the  first  form  of  the 
Wilson  producer  the  working  had  to  be  stopped  periodically 
to  enable  the  "clinker"  to  be  removed.  This  has  now 
been  got  over  entirely  by  the  use  of  a  water  bottom,  through 
which  the  ashes  can  be  removed  without  interfering  with 
the  working.  In  one  form  an  ash  discharger,  in  the  form  of 
an  inclined  screw,  in  addition  to  the  water  bottom,  is  used  ; 
the  screw  forms  the  bottom  of  the  receptacle  into  which  the 
ashes  fall  from  the  grate  bars,  and  as  they  collect  in  the 
spaces  between  the  threads  the  motion  of  the  screw  works 
them  forward  to  the  discharge  hole  below  the  level  of  the 
water  seal.  The  modern  producer  may  be  worked  con- 
tinuously until  it  is  stopped  for  repairs. 

The  use  of  caking  coal  in  the  producer  tends  to  the 
formation  of  a  dense  solid  mass  of  coke,  which  prevents  the 
proper  penetration  of  the  gaseous  current,  and  the  working 
is  unsatisfactory.  This  difficulty  is  got  over,  in  one  pro- 
ducer at  least,  by  the  introduction  of  a  mechanical  arrange- 
ment for  breaking  up  the  coke,  and  so  preventing  it 
clotting  into  a  solid  mass.  A  free  burning  coal  always 
gives  good  results. 

The  original  Siemens  producer  was  simply  a  deep  grate 
with  a  closed  top,  limited  bar  space,  and  an  open  ash  pit. 
It  was  then  modified  by  closing  the  ash  pit  and  blowing 
steam  into  it,  by  which  the  changes  shown  in  equations 
1  and  2,  p.  36,  are  increased.  It  has  been  further  modified 
by  forming  a  partition  between  the  hopper  and  the  gas  port, 
and  below  the  level  of  the  charge,  by  which  the  volatile 
matter  driven  out  of  the  fresh  coal  by  the  heat  of  the 
charge  below  is  forced  back  under  its  own  pressure  through 
the  glowing  fuel.  In  this  way  much  of  the  tar  is  split  up 


40  IEON  AND   STEEL. 

into  gaseous  compounds,  and  water  vapour  is  decomposed, 
so  that  the  trouble  due  to  tar  and  water  collecting  in  the 
mains  is  reduced,  and  the  gas  enriched. 

The  original  Wilson  producer  consisted  of  a  closed  cylin- 
drical chamber  with  an  arrangement  at  the  bottom  for  forcing 
in  air  by  a  steam  jet  blower,  by  which  the  proportion  of 
steam  to  air  could  be  regulated.  This  has  been  modified  by 


FIG.  4.— The  Duff-Whitfield  producer. 

carrying  off  the  gases  from  below  the  surface  of  the  charge, 
thus  causing  the  volatile  products  from  fresh  coal  to  be 
driven  back  through  a  hot  layer  of  the  charge  to  decompose 
the  tar  and  water.  It  has  also  been  further  modified  by 
the  introduction  of  a  water  bottom  in  place  of  the  old 
solid  bottom,  and  with  mechanical  means  of  removing  the 
ashes. 

The  Duff-  Whitfield,  producer  shown  in  vertical  section  in 
Fig.  4,  embodies  most .  of  these  improvements,  and  may  be 


MATEETALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  41 

taken  as  a  modern  type.  It  is  iron-clad,  and  lined  with 
refractory  brickwork.  The  horizontal  section  is  rectangular. 
The  fuel  is  charged  through  the  hopper,  A,  by  filling  it, 
closing  the  top,  and  then  lowering  the  conical  bottom  for 
the  charge  to  drop  into  the  body,  B,  which  is  thus  kept 
nearly  full.  The  heat  of  the  producer  cokes  the  fresh  coal, 
and  the  volatile  matter  from  it  is  drawn  off  by  the  steam 
jet,  C,  and  forced  into  the  hot  mass  below  ;  while  a  similar 
action  is  effected  lower  down  by  the  steam  jet,  D.  A  regu- 
lated quantity  of  air  blown  in  through  E,  passes  upwards 
through  the  sloping  grate  bars,  and  furnishes  the  oxygen 
for  carrying  on  the  production.  The  ashes  are  largely 
directed  outwards  by  the  sloping  grate,  and  fall  to  the 
bottom  of  the  water  seal,  F,  from  which  they  can  be  readily 
removed  without  interfering  with  the  working.  The  pro- 
ducer gas  is  drawn  into  the  gas  main  G,  through  which  it 
passes  to  the  furnace.  The  general  temperature  of  the 
gas  as  it  leaves  the  producer  is  about  500°C. ;  and  the 
volume  of  gas  formed  is  about  150,000  cubic  feet  per  ton  of 
coal  used. 

When  producer  gas  is  to  be  used  in  the  cylinders  of  gas 
engines,  in  the  place  of  coal  gas,  it  must  be  made  more 
carefully,  and  from  good  quality  fuel.  It  must  also  be 
"  cleaned  "  after  it  conies  from  the  producer,  and  for  this 
purpose  a  wet  scrubber  and  a  sawdust  scrubber  are 
required.  Also  a  gas  holder  for  storing  the  gas  is  neces- 
sary. These  requirements  have  led  to  the  modifications  of 
the  producer  when  used  for  gas  engine  work,  and  what  is 
known  as  the  suction  gas  producer  is  making  much  head- 
way. The  principal  modification  is  to  make  the  engine 
itself  regulate  the  quantity  of  air  and  steam  drawn  through 
the  producer,  and  therefore  the  quantity  of  gas  formed. 
Thus  an  increase  in  the  load  on  the  engine  causes  more  gas 
to  be  made  and  drawn  into  the  cylinder.  No  gasholder  is 
required,  and  the  cleaning  is  effected  by  a  wet  scrubber, 


42  IRON  AND   STEEL. 

An  evaporator,  in  which  water  is  kept  at  a  constant  level, 
surrounds  the  body  of  the  producer,  and  absorbs  heat  from 
it,  by  which  the  water  is  raised  nearly  to  boiling.  The 
supply  of  air  is  drawn  through  this  chamber  and  over  the 
hot  water  from  which  steam  rises  and  mingles  with  the 
air.  The  mixture  is  then  drawn  down  and  through  the 
closed  ash  pit  into  the  producer  to  generate  the  gas. 
Anthracite,  or  coke,  is  the  best  fuel  for  clean  working. 
"  Suction  "  gas  is  very  similar  in  composition  to  good  pro- 
ducer gas,  and  the  plant  is  being  used  to  work  engines  up 
to  75  h.-p.  But  this  limit  will  be  extended  in  the  near 
future. 

Mond  Gas. — An  important  point  in  the  making  of  Mond 
gas  is  in  the  salving  of  the  by-products,  especially  ammonia. 
This  is  effected  by  using  an  excess  of  steam,  so  as  to  keep 
the  temperature  as  low  as  possible  consistent  with  con- 
tinuous working,  and  so  prevent  the  ammonia  from  being 
decomposed  as  it  is  in  ordinary  producer  working.  The 
usual  condensing  and  scrubbing  plant  is  used  in  connection 
with  this  producer.  The  hot  gas  from  the  producer  passes 
through  a  series  of  channels  on  its  way  to  the  recovery 
plant,  and  heats  their  walls.  The  air  and  steam  on  their 
way  to  the  producer  are  driven  through  a  second  series  of 
channels,  in  which  they  come  into  contact  with  the  outer 
walls  of  the  first  series,  absorb  heat  from  them,  and  carry 
it  back  to  the  producer.  This  allows  of  a  much  larger  pro- 
portion of  steam  than  usual  being  used.  The  gas  is  cleaner 
and  less  poisonous  than  the  ordinary  gas,  and  should  come 
into  use  for  domestic  purposes. 

Water  Gas. — The  most  economical  method  of  producing 
water  gas  is  due  to  Messrs.  Dellwik  and  Fleischer,  and 
depends  on  the  fact  that  if  the  air  is  rushed  through,  even  a 
deep  layer  of  red-hot  coke,  the  carbon  is  rapidly  and  com- 
pletely burnt  with  the  production  of  a  very  high  temperature 
throughout  the  mass."  Very  little  carbon  monoxide  is  formed, 


MATERIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  43 

for  there  is  excess  of  oxygen  everywhere  throughout  the 
layer.  If,  then,  the  air  blast  is  cut  off  and  steam  turned  on, 
the  changes  already  described  will  take  place,  and  water 
gas  will  be  formed ;  but  this  soon  brings  down  the  tem- 
perature of  the  hot  coke,  and  in  a  short  time  the  steam 
must  be  cut  off  and  the  air  rushed  through  again.  Air  is 
blown  through  the  producer  for  one  minute  and  steam  for 
eight  minutes  alternately.  The  burnt  gas  passes  away  into 
a  chimney,  and  the  water  gas  is  drawn  off  for  use. 

REFRACTORY  MATERIALS. 

Refractory  materials  used  for  metallurgical  purposes  may 
be  denned  as  bodies  that  can  be  exposed  to  the  furnace 
temperatures  for  which  they  are  to  be  used  without  soften- 
ing or  disintegration.  The  well-known  compound  silica  in 
any  of  its  fairly  pure  natural  forms  is  a  very  refractory 
body,  and  may  be  exposed  to  the  furnace  temperatures  pro- 
duced by  the  combustion  of  ordinary  fuel  in  air  without 
softening.  It  will  withstand  a  clear  white  heat.  The  form 
very  suitable  for  refractory  purposes  is  quartz  when  it 
occurs  as  a  pure  sand,  sandstone,  or  quartzose  rock,  which 
often  contains  upwards  of  98  per  cent,  of  silica,  Si02. 

Silica  (p.  8)  is  an  acid-forming  oxide,  and  when  heated 
in  contact  with  basic  oxides  unites  with  them  to  form 
silicates  that  are  invariably  more  fusible  than  the  silica 
itself ;  but  the  actual  fusibility  of  these  bodies  depends 
upon  the  nature  and  proportion  of  the  basic  oxide  present. 
Thus,  given  silica  and  a  basic  oxide,  there  is  one  proportion 
between  them  that  has  a  higher  fusing  point  than  any 
other,  and  the  addition  of  either  one  or  other  of  the  oxides, 
within  limits,  lowers  the  fusing  point  of  the  mass.  If 
another  basic  oxide  is  added  the  fusibility  is  still  further 
increased,  and  it  may  be  taken  as  a  general  statement  that 
complex  silicates  are  more  fusible  than  simple  ones  of  the 
same  general  character.  The  range  of  fusibility  for  silicates 


44 


IRON   AND   STEEL. 


is  a  very  wide  one.  The  most  fusible  are  those  containing 
potash,  K20,  and  soda,  Na20,  and  the  least  fusible  those 
containing  alumina,  A1203. 

A  system  of  naming  silicates  that  has  been  largely 
adopted  by  metallurgists  depends  upon  the  proportion 
between  the  number  of  atoms  of  oxygen  in  the  acid  and 
basic  portions  of  the  silicate.  Clearly  this  is  based  upon 
the  assumption,  strongly  supported,  that  a  silicate  is  a 
combination  of  two  or  more  oxides,  one  of  which  is  always 
silica.  When  the  proportion  is  1  :  1  it  denotes  a  mono- 
silicate,  1 :  2  a  bisilicate,  1 :  3  a  trisilicate,  2 : 3  a  sesqui- 
silicate,  and  2  :  1  a  subsilicate.  These  relations  are  shown 
in  the  following  table,  in  which  they  are  illustrated  by  the 
silicates  of  lime  and  alumina  : 


Ratio    of    number    of 

1  :1 

Mono 

2CaO.Si02 

2Al208.3SiO2 

atoms  of  oxygen  in 

1:2 

Bi 

CaO.SiO2 

Al2O3.3iSOa 

basic  oxide  to  num- 

1:3 

Tri 

2Ca0.3Si02 

2Al203.9SiO2 

ber  of  atoms  of  oxy- 

2:3 

Sesqui 

4CaO.3Si02 

4Al2O3.9SiO2 

gen  in  acid  oxide. 

2:1 

Sub 

4CaO.Si02 

4Al203.3SiO2 

Experiments  made  at  ordinary  assay  furnace  temperatures 
show  that  among  the  silicates  of  lime  the  monosilicate  is 
the  least  fusible  and  the  bisilicate  the  most  fusible,  while 
the  silicates  of  alumina  are  infusible,  although  the  bisilicate 
shows  signs  of  softening  at  a  very  high  temperature.  Small 
quantities  of  other  bases  render  them  more  fusible. 

Clay. — The  principal  constituent  of  this  abundant  rock 
is  the  monosilicate  of  alumina  combined  with  water.  Clay 
beds  are  made  up  of  very  fine  particles  formed  by  the  dis- 
integration of  silicate  rocks  by  the  combined  action  of  air 
and  water,  and  then  deposited  as  a  sediment  similar  to 
other  sedimentary  rocks.  Very  often  the  clay  is  con- 
taminated with  oxide  of  iron,  lime,  potash,  and  soda,  in 
which  case  it  is  useless  for  refractory  purposes.  But  a  clay 


MATERIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  45 

associated  with  the  coal  measures,  and  usually  containing 
an  excess  of  silica,  with  only  small  quantities  of  other  oxides, 
is  very  refractory  in  character,  and  is  known  as  Jireclay. 
Its  composition  may  be  represented  generally  hy  the 
formula  xSi02.2Al203.3Si02.2H20,  where  xSi02  represents  a 
variable  proportion  of  the  acid  oxide.  This  clay,  in  common 
with  other  clays,  enjoys  the  property  of  plasticity  by  which 
it  can  be  moulded  into  shape  after  being  made  into  a  stiff 
paste  with  water.  When  heated  to  a  red  heat  the  combined 
water  is  driven  off,  and  the  clay  is  "burnt,"  after  which  it 
is  no  longer  plastic.  Considerable  shrinkage  takes  place  on 
burning,  and  to  counteract  this,  clay  already  burnt  is  mixed 
with  the  raw  clay  for  making  bricks,  crucibles,  &c.  The 
common  mixture  is  2  parts  of  raw  clay  to  1  part  of  burnt 
clay,  which  usually  consists  of  old  bricks  and  pots  cleaned 
and  ground  up  for  the  purpose. 

The  sandstones  are  not  sufficiently  plastic  when  mixed 
with  water,  although  they  usually  contain  a  small  propor- 
tion of  clay  in  admixture  with  the  silica.  The  material 
could  be  moulded,  but  when  dried  and  burnt  would  break 
down  too  readily.  In  this  case,  when  used  for  making  very 
refractory  silica  bricks,  a  small  proportion  of  fireclay  is 
added,  or  the  ground  material  is  mixed  with  milk  of  lime 
sufficient  to  carry  in  about  1  per  cent,  of  the  oxide.  When 
moulded  and  burnt  such  bricks  are  somewhat  friable,  but 
the  lime  fluxes  with  a  small  quantity  of  the  silica  and  forms 
a  cement  which  holds  the  particles  of  silica  together,  and 
makes  the  brick  coherent.  The  following  table  on  p.  46 
shows  the  composition  of  various  clays,  sandstones,  and  sands 
suitable  for  furnace  building  and  working : 

It  will  be  noticed  that  the  examples  of  fireclays  given 
contain  varying  proportions  of  silica,  and  when  the  silica 
runs  high  it  is  not  necessarily  all  in  combination  ;  part  of  it 
may  be  in  the  form  of  sand,  and  can  be  separated  by  careful 
washing  from  the  homogeneous  clay.  Fireclays  rich  in  silica 


46 


IKON  AND   STEEL. 


are  acid  in  character,  but  when  the  ratio  of  silica  to  alumina 
approaches  9:10,  which  is  roughly  the  composition  of  the 
monosilicate,  they  are  regarded  as  neutral  material.  White 
Coinish  clay  (Kaolin)  is  the  nearest  approach  to  the 
neutral  composition. 

Ganister  is  sufficiently  binding  to  be  used  for  some  pur- 


Fireclays.                                      Silica  Rocks. 

1 

03 

t"2 

c~ 

2 

3u 

"o  *^ 

03 

Constitiients. 

si 

^ 

tc£ 

.52 

S£ 

1 

1 

~  « 

o 

SJ§ 

eS 

r-ri 

11 

1 

|o 

ll 

2 
o 

1 

Silica,  SiO2       . 

65-10 

63-57 

48-04 

98-31 

94-6 

98-51 

Alumina,  AlaOs 

22*22 

27-45 

34-47 

0-72 

1-4 

0-51 

Ferric  Oxide,  Fe-2O8. 

0-15 

3-05 

0-18 

0-9 

0-07 

Ferrous  Oxide,  FeO. 

1-92 

Lime,  CaO 

0-14 

0-55 

0-66 

0.22 

0-5 

0-13 

Magnesia,  MgO 
Alkalies,  Na.2O,  K-2O 

0-18 
0-18 

0-45 

0-14 

0-2 

o-i 

0'0(i 
0-33 

Water,  H2O      . 

9*86 

9-91 

11-15 

0-50 

2-7 

poses  without  admixture,  as  it  contains  from  2  to  3  per  cent, 
of  clay. 

The  other  oxides  present  vary  from  2  to  4  per  cent.  They 
are  all  fluxing  in  character,  and  the  alkalies  are  the  most 
injurious. 

Basic  Materials. — The  term  basic  as  applied  to  refractory 
materials  implies  that  these  bodies  contain  basic  oxides, 
that  is,  oxides  which  react  with  acids  to  form  salts.  The 
principal  basic  oxides  of  a  refractory  character  are  lime, 
magnesia,  and  alumina.  Lime  and  magnesia  are  not  found 
in  the  free  state.  They  are  combined  principally  with 
carbon  dioxide  in  carbonates,  with  silica  in  silicates,  and 
with  sulphuric  oxide  in  sulphates.  Gypsum  is  the  well- 
known  sulphate  of  lime,  and  Epsom  salts  is  sulphate  of 
magnesia. 


MATERIALS  USED  IN  IRON  AND  STEEL  MANUFACTURE.  47 

Carbon  dioxide  can  he  driven  off  by  calcining  the  carbon- 
ates at  a  red  heat,  so  that  there  is  no  difficulty  in  obtaining 
the  basic  oxides  in  the  free  state. 

limestone  is  one  of  the  commonest  rocks  in  the  earth's 
crust,  and  is  found  in  huge  masses  among  the  rocks  belong- 
ing to  the  carboniferous  period.  Carbonate  of  lime 
CaO.C02,  is  the  principal  constituent  of  limestone,  marble 
and  chalk.  The  difference  in  the  physical  properties  of 
these  bodies  is  due  to  the  manner  in  which  they  were 
deposited,  and  to  the  difference  in  the  temperature  condi- 
tions to  which  they  were  exposed  through  long  periods  of 
time.  What  the  metallurgist  has  to  consider  is  the  nature 
and  proportions  of  the  impurities  present.  When  lime- 
stone is  strongly  heated  it  is  decomposed  thus  : 

CaO.C02  =  CaO  +  C02 

Lime 

Dolomite,  or  magnesian  limestone,  is  a  rock  containing 
carhonates  of  lime  and  magnesia.  When  these  are  present 
in  molecular  proportions  the  composition  may  be  repre- 
sented thus :  CaO.Mg0.2C02.  The  proportions  of  the  two 
carbonates,  however,  vary  somewhat  in  different  samples. 
Dolomite  does  not  occur  to  anything  like  the  same  extent 
as  limestone,  but  it  is  found  in  sufficient  quantities  to  form 
a  very  useful  refractory  material.  When  strongly  heated 
it  is  decomposed  as  follows : 

CaO.Mg0.2C02  =  CaO.MgO  +  2  C02 
Dolomite  Lime 

Magnesite. — This  rock,  which  is  not  widely  distributed, 
is  nearly  pure  carbonate  of  magnesia,  MgO.C02.  When 
strongly  heated  magnesia  is  obtained  thus : 

MgO.C02  =  MgO  +  C02 

Magnesia 
It  is  a  very  valuable,  but  expensive,  refractory  material. 


48 


IKON  AND   STEEL. 


Bauxite.  The  principal  constituents  of  bauxite  are  ferric 
oxide  and  alumina.  It  may  be  regarded  either  as  an  iron 
ore  or  as  a  flux,  and  is  also  largely  used  in  the  extraction  of 
aluminium.  It  is  white  to  whitish  brown  in  colour,  friable, 
and  refractory.  The  chief  sources  of  supply  in  Europe  are 
France  and  Ireland. 

The  following  table  gives  the  general  composition  of  the 
commoner  basic  materials,  and  will  serve  as  a  guide  : 


Limestone. 

Dolomite. 

Magnesite. 

Bauxite. 

Lime,  CaO    .... 

54-82 

34-2 

1-8 

Magnesia,  MgO    . 

0-22 

19-8 

42-7 

.  —  . 

Alumina,  A1203. 
Ferric  Oxide,  Fe2O3 

j    0-22 

I   - 

;  4, 

52-0 
27'6 

Carbon  Dioxide,  C02    . 

43-07 

43-4 

50-0 

.  — 

Silica,  Si02   .... 

0-36 

1-2 

1-0 

— 

Alkalies,  Na202,K20     . 

0-14 

— 

—  - 

— 

Water,  H20 

0-26 

— 

— 

20-4 

Neutral  Materials. — Bodies  that  are  refractory  in  character 
and  also  indifferent  to  the  fluxing  action  of  either  basic  or 
acid-forming  oxides  are  termed  neutral  materials.  Fireclay, 
approximating  to  the  monosilicate  in  composition,  is  usually 
regarded  as  neutral  material,  although  it  does  not  resist 
fluxing  action  very  well. 

Graphite,  or  plumbago,  is  a  natural  crystalline  form  of 
carbon  produced  by  the  metamorphosis  of  vegetable  matter. 
It  is  found  associated  with  the  oldest  rocks,  and  seems  to 
have  gone  a  stage  further  than  anthracite,  as  it  contains  no 
gaseous  matter.  It  practically  consists  of  carbon  and  ash- 
forming  matter,  which  varies  considerably  in  different 
samples.  It  is  not  as  widely  distributed  as  coal,  but  con- 
siderable deposits  are  found  in  different  parts  of  the  world. 
A  rich  deposit  existed  in  Cumberland,  but  is  now  largely 
worked  out.  The  most  abundant  supplies  at  present  come 


MATERIALS  USED  IN  IKON  AND  STEEL  MANUEACTUKE.  49 

from  Ceylon,  America,  Siberia,  and  Styria.  It  is  also  an 
artificial  product  of  the  electric  furnace,  and  is  then  pre- 
pared from  anthracite.  Its  principal  use  as  a  refractory 
material  is  in  the  manufacture  of  plumbago  crucibles,  the 
best  of  which  contain  about  30  per  cent,  of  the  prepared 
graphite  together  with  the  usual  clay  mixture.  It  is 
absolutely  infusible  at  the  highest  furnace  temperature,  and 
if  excluded  from  the  air  is  indestructible.  The  following 
examples  will  give  an  idea  of  the  variations  in  the 
composition  of  the  natural  material  :— 

Styrian  graphite,  carbon  79  per  cent. ;  ash  21  per  cent. 

Ceylon  graphite,  carbon  90  per  cent. ;  ash  10  per  cent. 

Chrome  Iron  Ore,  or  chromite,  is  the  most  abundant  ore 
of  the  useful  metal  chromium,  and  is  found  in  Scotland, 
France,  Germany,  Greece,  Eussia,  and  America.  The 
principal  compounds  present  are  oxides  of  iron  and  chro- 
mium. It  is  a  dark  coloured,  heavy,  hard,  refractory  stone, 
and  is  represented  by  the  formula  FeO.Cr20;>  It  is  infusible 
at  ordinary  furnace  temperatures,  and  is  used  to  a  limited 
extent  as  a  refractory  material,  but  much  more  as  an  ore  of 
the  metal  chromium. 

Ores  of  Ear e  Metals.— The  rare  metals  tungsten,  molyb- 
denum and  vanadium  have  come  into  use  in  some  branches 
of  steel  manufacture,  and  a  short  description  of  their  sources 
of  supply  will  be  found  useful. 

Wolframite  is  the  chief  ore  of  tungsten,  and  is  usually 
found  associated  with  tin  ore,  from  which  it  is  readily 
separated.  It  is  a  compound  of  the  acid-forming  oxide  of 
tungsten  with  ferrous  oxide,  and  has  the  formula  FeO. WO.,. 
The  ferrous  oxide  is  sometimes  partly  replaced  by  manganous 
oxide,  MnO. 

Molybdenite,  the  chief  ore  of  molybdenum,  contains  the 
metal  as  the  disulphide,  MoS2,  which  is  easily  converted 
into  the  oxide  by  a  simple  roasting  in  the  presence  of  air. 
It  is  found  in  Bohemia  and  Sweden. 


50  IEON  AND   STEEL. 

Vanadinite  is  the  important  ore  of  vanadium,  and  is  a 
chloro-vanadinate  of  lead.  It  is  found  in  Europe  princi- 
pally in  Spain,  in  Arizona,  and  Mexico.  The  metal  is  also 
present  as  oxide  in  some  sandstones,  and  in  this  way  is 
somewhat  widely  distributed.  The  vanadiferous  sandstones 
of  America  are  the  most  important.  The  ash  obtained  by 
burning  the  anthracite  from  the  Yauli  deposits  in  Peru  is 
very  rich  in  vanadium,  and  will  probably  be  used  as  a 
source  of  the  metal,  but  at  present  the  deposits  are  some- 
what inaccessible. 

All  these  metals  form  acid  oxides,  and  they  are  concen- 
trated as  such  by  fusing  the  concentrated  ores  with 
carbonate  of  soda  (Na2C03)  and  coal.  The  oxides  are 
thus  converted  into  soluble  soda  compounds,  and  can  then 
be  dissolved  out  of  the  insoluble  matter.  They  are  sepa- 
rated as  oxides  from  their  solutions  by  combining  the  soda 
with  a  stronger  acid,  such  as  sulphuric  acid,  and  are  then 
in  a  good  condition  for  the  extraction  of  the  metals. 


CHAPTEK  III. 

PRIMITIVE    METHODS    OF    IRON    AND    STEEL    PRODUCTION. 

Historical. — The  most  ancient  method  for  the  extraction 
of  iron  from  its  ores  and  adapting  it  to  the  use  of  man 
originated,  without  doubt,  in  the  East ;  and  India  was  most 
probably  the  seat  of  this  primitive  manufacturing  process. 
It  has  been  remarked  that  by  the  artificial  production  of 
fire  primitive  man  passed  the  barrier  which  now  exists 
between  the  human  race  and  the  rest  of  the  animal  king- 
dom, and  it  is  certain  that  when  he  could  use  this  source 
of  power  with  intelligence  the  extraction  of  the  common 
metals,  among  them  iron,  became  possible.  But  when  and 
where  the  possibility  became  an  accomplished  fact  is  lost 
in  the  mists  of  time,  for  the  faculty  of  doing  things  was  no 
doubt  antecedent  to  that  of  recording  them. 

In  order  to  follow  the  working  of  these  primitive  processes 
it  is  necessary  to  understand  the  principles  upon  which  they 
depend.  Bed  hasmatite  and  magnetite  are  the  purest  ores 
of  iron,  and  as  they  often  outcrop,  they  are  easily  accessible. 
The  gangue  is  siliceous,  so  that  to  obtain  the  iron  in  the 
metallic  state  the  oxygen  must  be  removed  from  its  chemical 
combination  with  the  iron,  and  the  silica  from  its  mechanical 
mixture  with  the  reduced  metal.  Either  carbon  or  carbon 
monoxide  will  combine  with  the  oxygen  at  a  red  heat.  For 
a  piece  of  red  haematite,  when  imbedded  in  red-hot  charcoal, 
has  its  iron  set  free  ;  but  the  silica  is  still  intermixed  with 
the  reduced  metal,  and  renders  it  useless.  If,  however,  the 
temperature  is  increased,  part  of  the  iron  compound  is  first 
reduced  to  ferrous  oxide,  which  unites  with  the  silica  to 

E  2 


52  IEON  AND   STEEL. 

form  a  fusible  compound ;  at  the  proper  temperature  the 
whole  mass  becomes  pasty,  and  part  of  the  fluid  cinder 
drips  out.  If  then  the  spongy  mass  is  well  hammered,  the 
fluid  matter  still  remaining  is  squeezed  out,  and  the  pasty 
metal  obtained  as  a  compact  malleable  mass.  The  changes 
taking  place  are  expressed  by  the  equations — 

C    +    02  =    C02;      C02    +    C    =     2CO. 

Carbon    Oxygen     Carbon     Carbon     Carbon       Carbon 
Dioxide    Dioxide  Monoxide 

2Fe203  +   3C  =  4Fe  +   3C02. 

Oxide  of  Iron    Carbon       Iron     Carbon  Dioxide 

Fe203    +   Si02  +  CO  =  2FeO.Si02   +  C02. 

Oxide  of  Iron     Silica       Carbon        Iron  Cinder          Carbon 
Monoxide  Dioxide 

It  is  thus  seen  that  the  changes  are  simple  in  character, 
and  not  at  all  difficult  to  control ;  and  it  is  easy  to  picture 
a  primitive  man  in  some  iron-bearing  district  using  lumps 
of  iron  ore  for  his  fire  stones,  and  after  an  unusually  brisk 
fire  finding  a  pasty  lump  of  metal  from  which  the  cinder  had 
dripped  out.  He,  like  his  modern  representative,  being  of 
an  inquisitive  turn  of  mind,  would  hammer  it  with  his  flint 
hammer,  and,  finding  it  pliable,  would  be  led  to  further 
trials,  ending  in  the  discovery  of  the  method  of  extracting 
iron  from  its  ore.  Now,  such  a  discovery  would  fill  several 
pages  in  the  proceedings  of  some  learned  society ;  then,  it 
was  probably  registered  by  a  few  gashes  on  the  nearest  tree 
trunk. 

Iron  Manufacture  in  India. — Large  deposits  of  easily 
reducible  ores  occur  in  many  of  the  hilly  districts  of  India  ; 
and  the  Hindoos  have  always  been  notable  workers  in  iron. 
The  extraction  of  the  metal  was,  however,  almost  entirely 
carried  on  by  hill  tribes  of  low  caste ;  and  it  is  difficult  to 
conceive  of  any  simpler  smelting  process  than  that  still  in 
operation  among  them — a  process  which,  with  very  little 


DIRECT  METHODS  OF  IEON  AND  STEEL  PRODUCTION.  53 

modification,  has  been  in  existence  for  several  thousand 
years.  The  piling  of  stones  round  and  above  the  surface 
of  the  fire  to  form  a  rough  shaft  or  chimney  would  soon 
come  into  use  as  the  increased  briskness  of  the  fire  due  to 
the  increased  draught  was  noticed ;  also  the  increased  heat 
of  the  fire  after  the  wood  had  charred  would  lead  to  the  use 


FIG.  5. — Iron  Smelting  in  India. 

of  charcoal  for  special  purposes.  And  so  all  the  essentials 
for  successful  working  would  be  obtained.  Then  the  use 
of  a  more  rapid  current  of  air,  obtained  either  by  natural 
means  or  by  blowing,  would  come  into  operation,  and  more 
rapid  working  would  result. 

The  smelting  furnace  may  be  described  as  a  circular 
shaft  built  of  refractory  stone,  and  daubed  over  with  clay 
to  make  it  airtight ;  or  it  is  made  entirely  of  fireclay 


54  IRON  AND   STEEL. 

plastered  inside  a  frame  of  stakes  driven  into  the  ground  to 
act  as  a  support  for  the  clay  until  it  sets.  Such  a  furnace 
has  an  internal  diameter  of  one  or  two  feet,  being  a  little 
narrower  at  the  top,  and  a  height  of  four  feet.  A  hole  at 
the  bottom  serves  to  run  off  the  liquid  cinder,  and  another 
a  little  higher  up  for  the  introduction  of  the  blast  pipe,  a 
bamboo  tube,  to  convey  the  blast  from  a  pair  of  primitive 
bellows  made  of  goat  skin  or  buffalo  hide. 

Fig.  5  is  the  reproduction  of  a  sketch  of  a  native  iron- 
works at  Nania  Bathan,  made  on  the  spot  by  Mr.  I.  E.  Lester 
as  recently  as  1897. 

The  ore  and  charcoal  are  put  in  through  the  top  of  the 
furnace,  and  the  fire  urged  for  several  hours ;  the  pasty 
mass  of  iron,  wet  with  the  liquid  cinder,  is  lifted  out 
through  the  top.  It  is  then  hammered  while  still  hot  to 
squeeze  out  the  greater  part  of  the  cinder  and  to  obtain  the 
metal  in  a  solid  lump.  Such  lumps  of  malleable  iron, 
weighing  from  five  to  thirty  pounds,  were,  and  are  still,  the 
finished  products  of  these  primitive  ironworks.  They  are 
sold  to  artificers,  who  fashion  them  into  various  shapes. 
The  cinder  is  collected  in  heaps  and  left  as  waste,  and 
deposits  in  various  parts  of  the  country  show  that  the 
workers  have  wandered  from  place  to  place  in  search  of  ore 
and  fuel.  As  a  matter  of  fact,  the  native  worker  takes  as 
little  trouble  as  possible  in  procuring  his  materials,  and 
will  only  work  those  portions  of  the  outcrop  that  have 
weathered  and  broken  down  into  small  pieces.  He  will  not 
trouble  to  mine  and  crush  the  ore,  and  so  moves  on  until 
he  finds  a  deposit  of  suitable  ore  and  wood  for  charcoal. 

When  a  narrow  ravine,  through  which  the  wind  blows  in 
a  fairly  constant  direction,  is  available  a  furnace  is  erected 
at  its  head,  and  the  natural  draught  through  the  ravine 
made  to  take  the  place  of  bellows. 

The  Hindoos  also  employed  a  primitive  method  for  the 
conversion  of  iron  into  steel,  viz.,  by  melting  small  charges 


DIRECT  METHODS  OF  IRON  AND  STEEL  PRODUCTION,  oo 


of  iron  mixed  with  wood  and  leaves,  and  thus  produced 
excellent  steel  from  which  weapons  and  cutting  tools  were 
made. 

The  Assyrians  and  Egyptians,  and  probably  the  Jews, 
obtained  their  iron  from  India  at  a  very  early  period ;  later 
the  Greeks  and  Eomans  received  supplies  of  the  metal 
from  the  Chalybes, 
a  tribe  living  and 
working  on  the 
south  coast  of  the 
Black  Sea. 

As  the  process 
migrated  westward 
it  was  improved  by 
the  greater  energy 
of  the  Western  races. 
The  Etruscans 
mined  the  haema- 
tite ore  of  Elba, 
and  extracted  the 
metal  by  a  process 
similar  to  that  still 
in  use  in  some 
remote  districts  of 
the  Pyrenees.  Fro-  6-The  Catalan  Fo'»e- 

The  Catalan  Process. — This  method  takes  its  name  from 
the  province  of  Catalonia.  The  furnace  used  is  an  open 
hearth  built  of  rough  masonry,  and  is  shown  in  I^ig.  6. 
The  bottom  and  back  of  the  hearth  A  are  formed  of  sand- 
stone blocks,  and  the  two  sides  are  lined  with  iron  slabs. 
The  front  or  working  side  consists  of  two  iron  plates,  the 
lower  one  of  which  is  perforated  by  a  tap  hole  for  running 
off  the  molten  cinder,  whilst  the  upper  one  is  used  to 
support  the  bar  required  in  the  manipulation  of  the  charge. 
The  blast  is  supplied  by  a  trompe  worked  by  the  water 


^^^ 


56  IRON  AND   STEEL. 

from  a  mountain  stream.  The  upper  cistern  B  is 
connected  with  the  lower  cistern  C  by  wooden  pipes,  about 
15  feet  long,  the  tops  of  which  are  perforated  by  air-holes 
inclined  downwards;  the  outlet  from  B  is  fitted  with  a 
conical  valve  worked  by  the  lever  D.  The  cistern  C  has 
a  closed  top,  and  an  outlet  at  the  bottom;  it  thus  forms  an 
air-chest  connected  directly  with  the  copper  blast-pipe,  or 
twyer,  E.  When  water  is  allowed  to  fall  through  the  pipe 
from  B  it  draws  in  air  through  the  air  channels  at  the  top, 
carries  it  down  into  the  chest  below,  and  forces  it  through 
the  blast  pipe  into  the  hearth.  The  strength  of  the  blast 
is  regulated  by  raising  and  lowering  the  valve.  Sometimes 
two  air  pipes  are  used  for  better  control  of  the  blast.  The 
whole  arrangement  is  usually  built  on  a  hillside. 

In  working  the  process,  charcoal  is  thrown  into  the  hot 
hearth,  and  moved  up  to  the  twyer  side  ;  then  iron  ore  is 
introduced,  and  the  whole  covered  with  moistened  charcoal 
dust  and  small  ore.  The  blast  is  then  partially  turned  on, 
and  the  full  charge  of  ore  gradually  added.  In  two  hours 
the  hearth  is  in  full  blast,  and  the  charge  is  being  worked 
from  the  side  towards  the  twyer.  The  molten  cinder  is 
tapped  away  at  intervals,  and  in  about  four  hours  the 
reduction  is  complete.  The  bloom,  as  the  mass  of  pasty 
iron  is  called,  weighing  about  300  pounds,  is  broken  up 
into  smaller  blooms,  which  are  then  taken  to  the  hammer 
and  thoroughly  hammered  to  squeeze  out  the  molten  cinder 
as  far  as  possible,  and  form  the  metal  into  rough  bars. 
These  bars  are  re-heated  and  hammered  to  render  them 
more  homogeneous.  The  cinder,  which  contains  upwards  of 
50  per  cent,  of  iron,  is  a  waste  product  as  far  as  this  method 
is  concerned. 

The  conditions  in  the  furnace  are  favourable  to  the  forma- 
tion of  carbon  monoxide,  and  this  gas,  in  conjunction  with 
the  charcoal,  reduces  the  oxide  of  iron  partly  to  the  metallic 
state  and  partly  to  ferrous  oxide,  which  unites  with  the  silica 


DIRECT  METHODS  OF  IRON  AND  STEEL  PRODUCTION.  57 

to  form  the  cinder  (see  p.  52).  The  twyer  is  inclined  so 
as  to  blow  into  the  hearth,  and  exert  a  refining  action. 
The  inclination  of  the  twyer  is  decreased,  so  that  it  may 
blow  more  across  the  hearth  than  into  it,  when  steel  is  to 
be  produced.  This  is  assisted  by  tapping  the  cinder  away 
at  more  frequent  intervals,  so  that  the  metal  is  more 
exposed  to  the  hot  charcoal  and  absorbs  carbon  from  it. 
Much  of  the  iron  and  steel  used  by  the  Spaniards  in  the 
zenith  of  their  power  came  from  this  source. 

The  American  Bloomery. — According  to  Howe,  a  hearth 
called  a  bloomery  is  still  in  use  in  America  to  work  up  a 
pulverised  and  washed  ore  of  good  quality,  using  charcoal 
as  fuel.  The  hearth  is  nearly  square,  in  horizontal  section, 
and  is  about  two  feet  wide  and  one  foot  deep  below  the 
twyer ;  it  is  formed  of  cast-iron  plates,  two  of  which,  the 
bottom  plate  and  the  back  plate  through  which  the  twyer 
enters,  are  hollow  for  the  circulation  of  water  to  keep  them 
cool.  These  hearths  are  usually  built  in  ranges  on  each 
side  of  a  quadrangular  mass  of  brickwork,  and  above  each 
hearth  is  a  heating  chamber  into  which  the  hot  gases  from 
the  hearth  pass,  and  in  which  is  a  coil  of  iron  pipe  for 
heating  the  blast  to  about  250°  C.  Charcoal  and  ore  are 
added  to  the  hearth  at  intervals,  and  a  loup  of  metal  some 
300  pounds  in  weight  is  produced  and  removed  every  three 
hours.  It  is  brought  in  front  of  the  twyer  to  be  further 
heated  before  it  is  taken  to  the  hammer  to  be  worked  up 
into  a  bloom.  The  cinder  is  tapped  at  intervals  through  a 
tap  hole  in  the  front  of  the  hearth. 

In  other  parts  of  Europe  the  early  furnaces  were  deeper 
than  the  Catalan  forge,  and  more  of  the  shaft  form.  They 
finally  culminated  in  the  high  bloomery,  a  furnace  of  some 
10  to  15  feet  in  height,  and  4  to  6  feet  internal  diameter  in 
the  middle,  but  narrower  towards  the  top  and  bottom.  It 
was  built  of  rough  masonry,  and  had  an  arched  opening  at 
the  bottom  which  was  loosely  bricked  up  during  the 


58 


IKON  AND  STEEL. 


working  of  a  charge.  The  blast  was  supplied  by  two 
twyers.  The  charge,  consisting  of  ore  and  charcoal,  was 
added  a  little  at  a  time  through  the  top  of  the  furnace  until 
the  full  charge  had  worked  down,  and  the  bloom  of  metal 
formed  in  the  hearth.  The  loose  bricks  were  then  taken 
out  and  the  bloom  removed  through  the  opening  thus 
made.  There  was  a  tap  hole  at  the  bottom  of  the  hearth 
through  which  the  cinder  drained  away.  The  general 

form    of    the    furnace    is 
shown  in  Fig.  7. 

In  shallow  hearths  the 
spongy  metal  soon  found 
its  way  to  the  bottom,  and 
was  protected  from  the 
action  of  the  carbon  by 
the  fluid  cinder,  which  also 
exerted  a  refining  action 
by  removing  carbon 
already  absorbed  by  the 
metal.  But  in  the  tall 
bloomeries  the  iron  was 
longer  in  contact  with  the 
charcoal  and  absorbed 


FIG.  7. — The  High  Bloomery. 
A,  Shaft.  B,  Arch.  C,  Twyer holes. 


more  carbon,  thus  becoming  steely  in  character.  The  first 
sample  of  cast  iron  was  no  doubt  an  accidental  product  of 
one  of  these  furnaces  when  working  under  such  conditions 
that  more  than  2  per  cent,  of  carbon  was  absorbed,  and 
the  temperature  rose  high  enough  to  melt  the  metal. 

The  Osmund  Furnace,  which  comes  between  the  shallow 
hearth  and  the  high  bloomery,  was  in  use  in  the  North  of 
Europe  for  many  centuries,  and  is  probably  still  to  be 
found  in  remote  districts.  It  is  a  small  shaft  furnace 
worked  by  a  single  twyer,  and  was  extensively  used  to 
reduce  the  bog  ore  dredged  from  the  shallow  lakes  and 
rivers  of  the  district.  The  ore,  which  is  a  brown  haematite, 


DIRECT  METHODS  OF  IEON  AND  STEEL  PRODUCTION.  59 

was  air-dried,  mixed  with  wood  fuel  and  calcined  in  heaps. 
It  was  then  smelted  with  charcoal  for  the  production  of  a 
spongy  mass  of  iron  called  an  osmund,  from  which  the 
furnace  takes  its  name.  The  ore  is  somewhat  rich  in 
phosphates,  but  the  metal  produced  was  fairly  free  from 
phosphorus  on  account  of  the  refining  action  of  the  very 
fluid,  highly  basic  cinder  formed  in  the  operation.  A  tap- 
hole  was  provided  for  the  cinder,  and  the  front  of  the 
furnace  had  to  be  taken  down  to  remove  the  osmund. 

The  Husgafvel  Furnace. — The  chief  drawback  to  the 
working  of  the  Osmund  furnace  is  that  it  has  to  be  practi- 
cally blown  out  after  each  charge,  and  the  furnace  partially 
removed  and  replaced  before  a  fresh  charge  can  be  intro- 
duced. This  means  waste  of  time,  labour,  and  fuel,  and 
in  1875  Husgafvel  commenced  to  experiment  in  the 
direction  of  larger  furnaces,  more  rapid  removal  of  the 
metal  sponge,  and  larger  outputs.  The  outcome  of  this  is 
a  furnace  which  may  be  described  as  a  modern  high 
bloomery.  The  shaft  of  this  furnace  is  formed  of  a  double 
casing  with  a  space  between,  through  which  a  spiral 
partition  runs  from  the  top  to  the  bottom,  thus  converting 
the  space  into  a  spiral  pipe  through  which  air  is  blown  to 
furnish  the  blast.  The  blast  is  thus  heated  to  about  200°  C., 
and  is  regulated  by  dampers  placed  at  intervals  in  the 
spiral  space.  The  shaft  and  the  charge  are  thus  cooled 
while  the  air  is  being  heated.  The  hearth  is  movable,  and 
is  supported  on  trunnions  fixed  to  a  bogie  carriage  which 
can  be  run  in  and  out  from  the  shaft.  It  is  supported  on 
a  platform  directly  under  the  shaft,  which  can  be  raised  and 
lowered  by  a  hydraulic  ram.  The  joint  between  the  hearth 
and  the  shaft  is  luted  round  with  clay  when  the  former  is 
in  position.  There  are  four  tap-holes  one  above  another 
in  the  side  of  the  hearth,  through  which  the  slag  can  be 
tapped  at  different  levels.  There  are  also  four  twyers 
which  blow  into  the  hearth  in  pairs  at  different  levels,  the 


60 


IEON  AND  STEEL. 


lower  pair  being  in  blast  at  the  beginning  of  the  operation, 
and  the  upper  pair  when  much  metal  has  collected  in  the 
hearth.  The  slag  is  tapped  off  so  as  to  keep  the  metal 
just  covered.  Owing  to  the  shaft  being  kept  comparatively 

cool  the  reduction  takes 
place  very  largely  in  the 
lower  part  of  the  furnace, 
and  the  metal  does  not 
remain  long  in  contact 
with  the  charcoal,  so  that 
not  much  carbon  is  taken 
up,  and  even  this  is  in  part 
removed  by  the  oxidising 
character  of  the  blast 
from  the  inclined  twyers, 
and  the  fluid  cinder.  The 
charge  is  composed  of 
prepared  bog  ore  in  small 
pieces,  rich  cinder,  and 
charcoal,  and  is  fed  in  at 
the  top.  When  the  bloom 
has  collected  the  hearth  is 
run  away  and  another  run 
in  from  the  opposite  side. 
The  cinder  is  drained  away 


FIG.  8.— The  Husgafvel  Furnace. 

A,  Shaft.  />,  Blast  main. 

/?,  Spiral  space.      E,  Twyers. 
(\  Hearth. 


and    the  bloom,  removed 
by  rotating  the  hearth  on 
F,  Hydraulic  table,      the  trunnions  and  tipping 

it  out.    (See  Fig.  8.) 

The  slag  rarely  contains  more  than  18  per  cent,  of  iron, 
with  the  softest  iron  produced,  and  with  hard  irons  may 
run  as  low  as  7  per  cent.,  so  that  other  bases  must  be 
present  in  the  ores,  and  as  rich  cinder  is  used  this  also 
forms  a  source  of  iron.  The  ores  are  phosphoric,  but  if 
the  cinder  is  kept  basic  the  greater  part  of  the  phosphorus 


DIEECT  METHODS  OF  IRON  AND  STEEL  PRODUCTION.  61 

is  found  in  it,  and  at  the  same  time  the  metal  is  compara- 
tively free  from  carbon ;  this  is  effected  by  inclining  the 
twyers  so  as  to  blow  more  into  the  hearth.  This  is  general 
in  direct  methods,  for  the  passage  of  much  carbon  into  the 
iron  is  coincident  with  passage  of  phosphorus  into  the  metal 
when  the  ores  contain  phosphates.  Thus  the  more  perfectly 
the  metal  is  separated  from  the  ore,  and  the  smaller  the 
quantity  of  it  that  passes  into  the  cinder,  the  more  impure 
and  unworkable  it  is,  so  that,  unless  very  pure  ore  such  as 
magnetite  is  used,  the  metal  must  be  further  treated  for  the 
elimination  of  the  impurities,  and  the  basic  open  hearth, 
which  will  be  described  fully  later,  has  been  used  in 
conjunction  with  the  Husgafvel  furnace. 

Many  attempts  have  been  made  during  the  last  sixty 
years  to  produce  iron  by  direct  processes,  and  if  they  have 
failed  it  is  not  because  the  men  who  took  them  in  hand 
lacked  either  energy,  knowledge,  or  capital,  but  that  the 
output  is  so  small  relatively  that  it  is  only  under  very 
exceptional  conditions  that  such  processes  can  be  made 
to  pay. 

Thus  in  the  Chenot  Process  a  sponge  of  iron  sufficiently 
soft  to  be  cut  with  a  knife  was  produced.  The  furnace 
used  in  the  process  took  the  form  of  two  vertical  retorts 
about  28  feet  high,  6  feet  long,  and  18  inches  wide,  built 
side  by  side,  and  surrounded  by  a  firebrick  case  furnished 
with  the  necessary  flues  and  grate  for  heating  the  lower 
portions  of  the  retorts  externally  by  the  combustion  of  solid 
fuel.  A  rich  and  pure  ore  broken  into  small  pieces  and 
mixed  with  charcoal  was  charged  into  the  retorts.  Thirty 
cwts.  of  calcined  ore,  10  cwts.  of  charcoal,  and  26  cwts.  of 
coal  for  the  external  firing  were  used  for  the  production 
of  a  sponge  weighing  about  12  cwts.  About  six  days 
elapsed  from  the  commencement  of  the  firing  before  the 
sponge  was  ready  for  removal.  The  metal  was  so  finely 
divided  that  even  when  only  moderately  warm  it  would 


62  IRON  AND   STEEL. 

take  fire  on  exposure  to  the  atmosphere,  and  form  oxide  of 
iron  again.  A  rectangular  iron  cooler  at  the  bottom  of  each 
retort  was  used  to  prevent  the  metal  from  coming  into 
contact  with  the  air  until  sufficiently  cooled.  The  sponge 
could  be  compressed  when  cold,  reheated,  and  hammered 
or  rolled  into  bars. 

The  process  was  not  a  commercial  success,  and  even  the 
Blair  Process,  an  American  modification  of  it,  has  been 
abandoned.  Blair's  furnace  consisted  of  a  group  of  three 
vertical  cylindrical  retorts  four  feet  wide  and  forty  feet  high, 
each  having  a  brickwork  casing  lined  with  firebricks  so  as 
to  form  a  combustion  space  round  the  retort.  The  outside 
of  the  retort  was  heated  by  burning  producer  gas  in  this 
combustion  space,  and  as  the  external  heat  did  not  pene- 
trate to  the  centre  of  the  charge  it  was  assisted  by  a  jet  of 
burning  gas  driven  down  the  centre  of  the  retort  by  a 
blowpipe  arrangement  fixed  in  the  top  of  each.  A  water- 
jacketed  iron  cooler  was  arranged  at  the  bottom  of  the 
retort  to  receive  the  sponge  before  its  final  removal  to  be 
worked  up.  In  spite  of  several  modifications  in  which 
advantage  of  gas  firing  and  regeneration  was  taken,  the 
process  did  not  prove  a  commercial  success. 

The  Siemens  Rotator  Method  should  also  be  noted  as  a 
somewhat  recent  attempt  to  create  a  modern  direct  process 
for  the  extraction  of  iron.  It  was  used  to  some  extent 
both  in  England  and  in  America,  but  was  unable  to 
compete  with  advances  in  other  directions.  It  comprised 
the  regenerative  system  of  Siemens,  which  has  been 
already  referred  to  in  connection  with  fuel  and  will  be 
more  fully  dealt  with  later,  and  the  rotating  cylinder  of 
Danks.  The  reduction  chamber  consists  of  an  iron  cylinder 
lined  with  refractory  bricks  made  from  bauxite  mixed  with 
a  little  clay  and  plumbago.  It  could  be  rotated  on  a  hori- 
zontal axis  by  the  necessary  gearing,  and  was  so  arranged 
with  respect  to  the  producer  and  the  regenerators  that  the 


DIRECT  METHODS  OF  IRON  AND  STEEL  PRODUCTION.  63 

flame  from  the  combustion  of  the  producer  gas  could  pass  right 
through  it  and  into  a  movable  flue  at  the  other  end.  The 
fire  bridge  end  of  the  cylinder  was  protected  by  the  circu- 
lation of  water  through  it,  as  also  were  three  ribs  projecting 
above  the  lining  at  right  angles  to  the  axis  of  the  cylinder. 
These  were  used  for  the  separation  of  the  charge  into  three 
portions  at  the  end  of  the  operation.  The  ore  was  reduced 
by  coal  assisted  by  the  rotation  of  the  cylinder,  which  pro- 
duced thorough  mixture,  and  a  little  lime  was  added  to 
prevent  the  too  rapid  corrosion  of  the  lining.  A  fluid 
cinder  of  basic  character  was  tapped  away,  and  the  reduced 
metal  collected  into  three  sponges  by  the  protruding  ribs. 
The  sponges  were  removed  from  the  flue  end  of  the  cylinder 
by  pushing  aside  the  movable  flue,  and  passed  on  to  the 
forge  to  be  worked  up  into  bars. 

Iron  Manufacture  in  Africa. — Sir  Lothian  Bell,  in  his  work 
on  "Iron  and  Steel,"  states  that  Colonel  Grant  furnished 
him  with  a  sketch  of  a  primitive  forge  which  he  had  seen  at 
work  in  the  interior  of  Africa.  It  was  apparently  a  hole  in 
the  ground  supplied  with  ore  and  charcoal,  and  the  fire 
urged  by  the  blast  from  a  pair  of  primitive  bellows  worked 
by  two  natives.  The  smelting  charge  of  crushed  ore  and 
charcoal  was  added  in  small  portions  at  a  time  until  a 
bloom  of  sufficient  size  was  obtained.  The  product  of 
such  a  furnace  would  not  exceed  a  dozen  pounds  of  metal 
per  day. 

An  interesting  paper  on  the  same  subject  was  read  at  the 
meeting  of  the  Iron  and  Steel  Institute  in  1904,  by  Mr. 
C.  V.  Bellamy  in  which  he  describes  a  West  African  iron 
works,  consisting  of  a  few  huts,  but  producing  iron  high  in 
carbon  and  of  excellent  quality.  The  ore,  which  is  a 
siliceous  haematite,  is  found  just  below  the  surface,  and 
after  calcining  over  a  slow  wood  fire,  is  concentrated  by 
grinding  and  washing  to  60  per  cent,  metallic  iron.  The 
prepared  ore  is  then  reduced  in  a  small  cupola  furnace  built 


64  IEON  AND   STEEL. 

in  the  centre  of  a  hut  or  smelting  house.  The  cupola  is 
formed  entirely  of  clay,  and  consists  of  a  dished  out  circular 
hearth  below  the  floor  level  covered  with  a  domed  roof.  It 
is  about  seven  feet  in  external  diameter  and  four  feet  high. 
There  is  a  tap  hole  in  the  bottom  to  which  access  is  obtained 
by  a  tunnel  underneath  the  floor ;  also  there  are  a  number 
of  openings  round  the  side  above  the  floor  level,  and  inclined 
downwards  towards  the  centre,  one  of  which  is  larger  than 
the  others,  and  is  used  as  a  working  door.  The  tap  hole  is 
plugged  up  from  below  with  moist  sand,  and  clay  pipes  about 
one  inch  in  diameter,  two  to  each  opening,  are  inclined 
downwards  towards  the  centre  of  the  hearth.  Charcoal  is 
added  and  fired,  and  then  the  apertures  are  all  luted  up, 
when  a  current  of  air  is  drawn  naturally  down  the  pipes, 
while  the  products  of  combustion  escape  through  a  hole  in 
the  top  of  the  dome.  An  effective  natural  draught  is  thus 
obtained,  and  the  charging  is  commenced  by  the  addi- 
tion of  a  flux  of  rich  cinder,  after  which  ore  and  fuel  are 
added  at  intervals  through  the  hole  in  the  dome.  The 
cinder  is  tapped  away  from  time  to  time  through  the  hole 
in  the  bottom,  and  the  last  runnings  are  saved  for  flux. 
The  smelters  say  that  without  this  flux  they  are  unable  to 
carry  out  the  reduction,  and  are  careful  to  take  some  with 
them  when  they  change  their  location.  But  this  is  probably 
only  a  tradition.  At  the  end  of  thirty-six  hours  a  bloom  of  iron 
rich  in  carbon  is  obtained,  and  removed  through  the  larger 
opening  in  the  side  of  the  furnace.  When  it  is  cold  it  is 
broken  up  into  suitable  pieces  and  sold  to  the  smiths, 
who  decarburise  it  in  small  forges.  In  this  way  a  steel 
containing  about  1  per  cent,  of  carbon  is  obtained 
which  is  worked  up  into  tools  and  weapons.  The  tools 
used  by  the  smelters  themselves  are  very  primitive,  and 
are  made  of  wood  for  the  most  part;  iron  itself  is  used 
vary  sparingly. 

There  is  no  record  of  how  long  the  process  has  been  in 


DIRECT  METHODS  OF  IRON  AND  STEEL  PRODUCTION.     65 

use,  but  it  has  been  carried  on  by  the  same  tribe  for  many 
generations  ;  and,  like  the  Hindoo  smelters,  these  African 
ironworkers  have  moved  from  place  to  place  in  search  of 
ore  and  fuel.  On  finding  both  in  sufficient  quantity  they 
settled  on  the  spot,  and  remained  there  until  the  supplies 
were  worked  out. 

Great  Britain. — The  evidence  of  early  iron  manufacture 
in  this  country  is  mostly  objective,  for  the  written  records 
are  very  meagre.  But  in  nearly  all  parts  of  the  country 
where  iron  ores  are  found  there  are  found  also  deposits  of 
iron  cinder,  which  prove  conclusively  that  the  metal  was 
extracted  on  an  extensive  scale  in  early  times.  This  is 
supported  by  the  fact  that  the  Britons  who  opposed  the 
landing  of  the  Komans  some  two  thousand  years  ago  were 
supplied  with  iron  weapons.  That  these  were  home-made 
is  most  probable,  for  it  is  unlikely  that  Britons  were  import- 
ing the  metal  at  that  time,  whatever  we  may  do  now. 

The  Romans  seem  to  have  soon  discovered  the  methods 
in  use,  for  it  is  said  that  a  large  forge  for  military  purposes 
was  erected  at  Bath  to  work  up  supplies  of  iron  obtained 
from  various  parts  of  the  country.  Iron  smelting  must 
have  been  carried  on  very  extensively  in  the  Forest  of  Dean 
at  a  very  early  period,  for  cinder  deposits  rich  in  iron  were 
smelted  for  their  metal  in  the  more  modern  blast  furnaces 
during  a  period  of  300  years. 

An  extensive  deposit  of  rich  cinder  has  been  recently  dis- 
covered in  Warwickshire,  which  it  is  proposed  to  work  for 
the  metal ;  and  the  convergence  of  the  old  roads  in  the 
district  towards  the  deposit  seems  to  indicate  extensive 
workings,  although  there  is  at  present  no  evidence  in  these 
heaps  of  the  remains  of  furnaces  and  tools. 

The  presence  of  cinder  on  the  banks  of  streams  in  various 
parts  indicates  that  water  power  was  used  for  the  production 
of  the  blast,  and  for  forging ;  so  that  some  advance  must 
have  been  made  upon  the  primitive  process.  Whether  the 

i.s.  F 


66  IRON  AND   STEEL. 

Romans  worked  the  rich  deposits  of  Cumberland  haematite 
is  doubtful,  but  there  is  evidence  of  early  working  in  the 
district ;  and  the  Scots  during  their  frequent  incursions 
across  the  border  were  assiduous  collectors  of  iron,  which 
they  preferred  to  any  other  form  of  spoil.  The  internal 
dissensions  following  the  departure  of  the  Romans,  and  the 
constant  strife  during  the  Saxon  period,  must  have  interfered 
with  the  manufacture  of  the  metal,  and  the  advent  of  the 
Normans  also  checked  it  further,  for  it  is  stated  that  the 
iron  utensils  in  the  kitchens  of  Edward  III.  were  classed 
among  the  royal  jewels. 

Later,  Kent,  Sussex,  Northamptonshire,  and  the  Forest 
of  Dean  were  the  principal  seats  of  iron  manufacture,  and 
kept  this  country  well  to  the  front  among  the  iron  pro- 
ducers of  the  world  until  the  advent  of  cast  iron,  when  she 
gradually  took  the  lead,  and  maintained  it  until  1895. 


CHAPTER   IV. 

PIG    IRON    AND    ITS    MANUFACTURE. 

THE  metallurgical  chemist,  when  called  upon  to  analyse 
a  sample  of  commercial  iron,  always  looks  for  carbon, 
silicon,  manganese,  phosphorus,  and  sulphur,  in  addition  to 
iron,  and  when  more  than  2  per  cent,  of  carbon  is  present 
he  calls  the  metal  cast  iron. 

The  melting  point  of  pure  iron  (about  1600°  C.)  is  above 
the  working  temperature  of  any  of  the  furnaces  described 
in  the  last  chapter ;  and  although  the  passage  of  one  or 
more  of  the  elements  named  above  into  the  reduced  metal 
lowers  its  melting  point,  the  iron  produced  in  such  furnaces 
did  not  melt,  but  remained  in  a  semi-solid  or  pasty  con- 
dition, and  was  so  removed  from  the  furnace.  It  is  probable, 
however,  that  under  exceptional  conditions  a  charge  having 
absorbed  more  carbon  and  silicon  than  usual,  melted,  and 
was  run  from  the  furnace  in  the  molten  condition.  This  is 
supposed  to  be  the  origin  of  cast  iron ;  the  date  is  usually 
given  as  1350  A.D.,  and  the  locality  Germany. 

The  process  was  not  introduced  into  Great  Britain  until 
1500  A.D.,  when  furnaces  began  to  appear  in  districts  where 
a  plentiful  supply  of  wood  for  charcoal  could  be  obtained. 
For  more  than  a  hundred  years  cast  iron  was  produced 
solely  with  charcoal  in  this  country.  Then  in  1619  Dud 
Dudley  introduced  the  use  of  pit  coal  in  the  smelting  of  iron 
ores  for  cast  iron ;  but  it  was  not  taken  up  generally,  as  it 
was  not  a  success  in  the  hands  of  these  early  British 
ironworkers.  In  1713  Darby  commenced  to  use  coke  in 
the  blast  furnace,  which  very  rapidly  replaced  both  charcoal 

F  2 


68 


IBON  AND   STEEL. 


and  coal,  and  caused  a  transference  of  the  industry  from 
wooded  to  coal-producing  districts.  In  1740  there  were 
ahout  sixty  hlast  furnaces  at  work  in  this  country,  and  fifty 
years  later  the  number  had  increased  to  106,  of  which  81 
were  coke  furnaces  and  25  charcoal  furnaces.  The  weekly 

makes  were  very  small, 
about  10  tons  for  a 
charcoal  and  15  tons 
for  a  coke  furnace,  as 
compared  with  the 
enormous  yield,  upwards 
of  3,000  tons,  of  a  rapidly 
driven  American  furnace 
of  to-day. 

The  last  charcoal  fur- 
nace in  the  south  of 
England  w7as  blown  out 
in  1827,  and  in  Scotland 
in  1866  ;  but  some  sur- 
vived in  the  north  of 
England  until  a  few  years 
ago.  A  furnace  some  30 
feet  in  height,  and  pro- 
ducing 30  tons  of  metal 


FIG.  9.— Blast  Furnace  (Miller). 


per  week  from  a  working 
charge  of    charcoal,  red 

haematite,  Irish  aluminous  ore,  and  limestone,  was  in  use 

in  the  Ulverstone  district  as  late  as  1894. 

But  charcoal  furnaces  are  still  in  use  on  the  Continent  of 

Europe,  principally  in  Styria  and  Sweden,  and  in  North 

America  for  the  production  of  special  brands  of  iron.    Their 

existence,  however,  depends  upon  an  abundant  supply  of 

wood. 

As   the   use   of   coke   extended,  the  furnaces   gradually 

increased  in  capacity,  and  became  very  ponderous  struc- 


PIG  IEON  AND   ITS  MANUFACTURE.  69 

tures  on  account  of  the  supposed  necessity  for  very  thick 
walls  of  rough  masonry  surrounding  the  refractory  lining. 
These  furnaces  were  worked  with  open  tops,  and  the  large 
body  of  flame  issuing  from  them  was  a  familiar  sight  in  iron- 
making  districts  some  fifty  years  ago.  The  lurid  glare  in 
the  sky  at  night  in  the  "Black  Country,"  when  Stafford- 
shire was  the  busiest  iron-making  district  in  the  world,  was 
then  a  notable  feature.  Now  a  chimney  on  fire  would 
probably  do  more  to  attract  the  attention  of  the  passer-by 
than  a  modern  furnace  in  full  blast.  Fig.  9  shows  an  open- 
topped  blast  furnace  of  the  old  type. 

Preparation  of  Iron  Ores. — The  ore  as  it  comes  from  the 
mine  or  quarry  in  the  raw  state  may  or  may  not  be  fit  to 
pass  at  once  to  the  smelting  furnace.  Assuming  that  there 
is  enough  iron  in  it  to  render  its  extraction  profitable,  it  is 
then  necessary  to  determine  whether  the  ore  requires  any 
preliminary  treatment  before  it  is  smelted.  This  is  readily 
done  by  heating  an  average  sample  of  the  powdered  ore  to 
a  temperature  below  that  at  which  it  softens  and  clots 
together.  If  the  loss  is  considerable,  it  shows  that  there  is 
much  volatile  matter  present  that  should  be  got  rid  of  by  a 
preliminary  operation.  The  process  is  known  as  calcination, 
and  may  be  carried  on  in  heaps,  stalls,  or  kilns.  The  last 
of  these  is  the  modern  method,  and  the  best  for  general 
work.  The  calcination  of  clay  ironstone  furnishes  a  good 
illustration  of  the  changes  that  may  take  place  as  the 
operation  proceeds.  The  iron  is  present  in  the  form  of 
ferrous  carbonate,  FeO.C02,  and  when  this  compound  is 
raised  to  a  low  red  heat  in  contact  with  air  it  undergoes 
the  following  change  :— 

2FeO.C02  +  0  ==  Fe203  +  2C02. 
Ferric  Oxide 

Then  the  clay  of  the  gangue  loses  its  water  of  hydration, 
and  any  hygroscopic  moisture  is  also  got  rid  of. 


70  IEON  AND   STEEL. 

Any  iron  pyrites  present  loses  part  of  its  sulphur  thus  :— 

FeS2  -  FeS  +  S. 
Ferrous 
Sulphide 

And  the  liberated  sulphur  burns  to  form  sulphur  dioxide. 
Part  of  the  ferrous  sulphide  also  undergoes  change  in 
contact  with  excess  of  air. 

2FeS  +  70  =  Fe203  +  2S02. 

Sulphur  Dioxide 

Thus  clay  ironstone  loses  all  its  carbon  dioxide  and  water 
and  part  of  its  sulphur,  and  ferrous  oxide  is  converted  into 
ferric  oxide  ;  while  the  lumps  of  ore  are  rendered  more 
porous  by  the  escape  of  this  volatile  matter.  Blackband 
ironstone  loses,  in  addition,  the  bituminous  matter  it 
contains.  Brown  haematite  loses  water  and  part  of  its 
sulphur.  But  red  haematite  and  magnetite  have  very  little 
to  lose,  and  are  rarely  calcined.  Phosphates  are  not  affected 
by  the  process,  so  that  there  is  no  reduction  in  the  quantity 
of  phosphorus  present.  The  following  may  be  taken  as  the 
average  losses  of  various  ores  on  calcination  :—  blackbands, 
50  per  cent. ;  clay  ironstones,  27  per  cent. ;  brown  haematites, 
14  per  cent. ;  red  haematites,  6  per  cent. 

The  conversion  of  ferrous  oxide  into  ferric  oxide  is 
important,  as  the  higher  oxide  has  much  less  tendency  to 
flux  with  silica  than  the  lower  one,  and  iron  is  thus 
prevented  from  passing  into  the  slag.  The  following 
table  gives  the  approximate  percentages  of  the  principal 
constituents  of  a  clay  ironstone  before  and  after  calcina- 
tion, and  shows  the  general  effects  of  the  operation. 
It  will  be  noticed  that  the  escape  of  volatile  matter  causes 
an  increase  in  the  proportion  of  the  solids  in  the  residue. 


PIG  IRON  AND  ITS  MANUFACTURE. 


71 


« 

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11° 

feOfa 

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M 

33  55 

-Sl- 

IsS 

III 

"rt 
fJ 

Raw    

35 

5-5 

10 

5 

11 

18 

1-25 

10 

Calcined      .... 

— 

58-5 

13-5 

6-5 

14-5 

— 

1-65 

— 

Calcination  in  /i<?aps  is  carried  out  by  dumping  a  layer  of 
the  ore  on  the  selected  ground  and  covering  it  with  a  layer 
of  small  coal.  This  is  followed  by  alternate  layers  of  ore 
and  coal  until  the  heap  is  made  up.  Such  a  heap  may  be 
50  feet  wide,  6  feet  high,  and  200  feet  long,  and  may  con- 
tain about  2,000  tons  of  ore.  It  is  fired  at  one  end  and 
allowed  to  burn  out,  which  occupies  several  weeks.  From 
8  to  10  per  cent,  of  coal  is  used.  The  method  is  wasteful 
of  time,  labour,  and  fuel,  and  is  not  much  in  favour.  More 
sulphur,  however,  is  eliminated  than  by  other  methods. 
The  blackband  ores  of  Scotland  are  sometimes  calcined  in 
this  way,  and  they  contain  sufficient  coaly  matter  to  calcine 
without  the  addition  of  fuel. 

Calcination  in  stalls  is  equivalent  to  surrounding  a  small 
heap  of  ore  and  fuel  by  three  walls,  and  loosely  closing  up 
the  front  with  bricks  or  lumps  of  ore.  A  series  of  stalls  is 
made  by  building  a  number  of  short  walls  at  right  angles 
to  a  long  wall,  so  as  to  form  a  number  of  compartments. 
These  are  filled  with  the  ore  and  fuel,  the  fronts  loosely 
bricked  up,  and  the  charge  fired.  Air  gains  admission 
through  the  fronts,  and  the  calcining  proceeds  in  a  fairly 
uniform  manner.  The  ore  and  fuel  may  be  dumped  from 
trucks  running  on  rails  over  the  tops  of  the  stalls,  and  the 
calcined  ore  drawn  from  the  floor  level.  The  proportion  of 
fuel  to  ore  is  rather  less  than  for  heap  calcining. 

Calcining  in  kilns  is  most  largely  used,  and  is  more 
economical  than  either  of  the  other  methods.  Various 
forms  of  kilns  are  used,  but  they  mostly  belong  to  the 


72 


IEON  AND   STEEL. 


barrel  type  of  furnace.     Some  are  fired  with  solid  fuel,  and 
others  with  the  combustible  gas  from  the  blast  furnace. 

Gjers'  kiln  is  a  good  illustration  of  a  coal-fired  kiln,  and 
a  short  description  of  its  construction  and  mode  of  working 
will  furnish  sufficient  details  of  the  general  process.  The 
shell  of  the  kiln  consists  of  a  huge  iron  cylinder  tapered  off 
into  a  conical  portion  at  the  bottom,  and  formed  of  iron 

plates  riveted  to- 
gether. It  is  lined 
with  a  14-inch  course 
of  firebricks,  and  is 
closed  at  the  bottom 
by  a  circular  iron 
plate  supported  on 
short  pillars  about 
2J  feet  from  the 
ground.  A  cast  iron 
truncated  cone,  built 
up  from  the  floor 
level,  passes  through 
a  circular  hole  in  the 
bottom  plate  up  into 
the  body  of  the  kiln. 
The  top  of  this  cone 
is  surmounted  by 
another  slightly  wider 


FIG.  10.— Gjers'  Calcining  Kiln. 


cone  which  forms  a  kind  of  cap,  and  at  the  same  time  allows 
air  to  pass  between  the  two  into  the  kiln  without  risk  of  the 
air  space  being  stopped  up  by  dust  and  small  ore.  The 
bottom  plate  is  pierced  by  a  number  of  holes  that  serve  as 
discharging  doors;  and  in  the  conical  part  of  the  shell  is  a 
second  set  of  openings  which  serve  for  the  admission  of  air, 
and  for  the  insertion  of  iron  rods  to  break  up  any  obstruc- 
tion that  may  form  during  working.  The  top  of  the  kiln  is 
open,  and  has  sets  of  rails  passing  across  it,  on  which  trucks 


PIG  IKON   AND   ITS  MANUFACTUKE.  73 

containing  the  ore  and  fuel  can  be  run,  and  their  contents 
dumped  into  the  kiln.  Such  a  kiln,  24  feet  in  diameter  and 
88  feet  high,  has  a  capacity  of  about  8,000  cubic  feet,  and 
will  hold  some  250  tons  of  ore  and  fuel.  The  consumption 
of  fuel  is,  roughly,  1  ton  of  coal  to  25  tons  of  ore.  It  works 
continuously,  the  mixture  of  ore  and  fuel  passing  in  at  the 
top,  and  the  calcined  ore  being  raked  out  at  the  bottom. 
The  cone  serves  the  double  purpose  of  admitting  air  into 
the  centre  of  the  kiln  and  directing  the  calcined  charge 
outwards.  About  150  tons  of  ore  pass  through  the  kiln  per 
day.  Fig.  10  shows  the  general  form  of  the  kiln. 

Weathering. — Pyritic  and  shaly  ores  are  improved  by 
exposure  to  wind  and  rain.  This  is  termed  weathering, 
and  may  extend  over  months  or  even  years.  Iron  pyrites, 
FeS2,  is  slowly  oxidised  to  ferrous  sulphate,  FeS04,  which, 
being  soluble,  is  washed  away  by  the  rain.  Shaly  ore  is 
slowly  disintegrated,  and  the  useless  portions  can  be  picked 
out.  The  general  effect  of  weathering  on  a  spathic  ore  is 
to  convert  it  into  brown  haematite,  but  the  necessary 
conditions  are  not  always  present. 

Concentration. — Poor  ores  containing  magnetic  oxide, 
Fe304,  can  be  concentrated  by  passing  the  finely  divided 
material  through  magnetic  concentrators  in  which  power- 
ful electro-magnets  attract  the  iron  compound,  and  allow 
the  particles  of  non-magnetic  gangue  to  fall  into  a  hopper 
by  which  it  is  passed  out  of  the  machine.  The  magnetic 
particles  are  carried  by  revolving  drums  out  of  the  magnetic 
field,  when  they  fall  into  another  hopper,  and  pass  out  of 
the  machine.  Not  only  is  the  iron  concentrated  in  a  smaller 
bulk  of  material,  but  phosphates  and  pyrites,  which  are 
non-magnetic,  are  concentrated  in  the  gangue,  and  thus 
eliminated  to  a  considerable  extent.  The  concentrates  are 
mixed  with  some  binding  carbonaceous  material  and  pressed 
into  briquettes  for  the  blast  furnace.  Ores  containing  ferric 
oxide,  Fe->03;  which  are  non-magnetic,  may  be  rendered 


74  IRON  AND   STEEL. 

so  by  heating  to  a  low  red  heat  with  a  regulated  quantity 
of  ground  coal,  or  in  a  current  of  reducing  gas,  by  which 
the  oxide  is  reduced  to  the  magnetic  condition,  and  can 
then  be  concentrated. 


THE  SMELTING  OF  PIG  IRON. 

The  process,  which  is  not  a  very  complicated  one,  is 
carried  on  entirely  in  a  blast  furnace,  and  as  the  output  is 
very  large  it  is  also  a  cheap  process.  In  the  evolution  of 
the  modern  blast  furnace  as  used  in  the  smelting  of  iron 
ores  for  pig  iron  the  general  principle  has  been  but  slightly 
modified.  The  important  modifications  are  in  the  dimen- 
sions and  proportions  of  the  furnace,  and  in  the  method  of 
working.  Thus  in  the  earlier  furnaces  the  height  was  about 
three  times  the  greatest  diameter.  Since  then  the  height 
has  increased,  and  in  greater  proportion  than  the  width, 
and  now  the  height  is  about  four  times  the  greatest 
diameter.  According  to  Bidsdale,  the  modern  English 
furnace  varies  from  70  to  100  feet  in  height,  depending  upon 
the  general  conditions  of  working. 

The  Modern  Blast  Furnace. — One  of  the  first  requisites 
is  a  thoroughly  good  solid  foundation  to  carry  the  huge 
bulk  without  slipping.  If  the  ground  is  at  all  loose,  piles 
must  be  driven  in  to  make  it  firmer.  The  main  shell  of 
the  furnace  consists  of  a  huge  cylinder  formed  of  curved 
iron  plates,  half  an  inch  thick,  riveted  together,  and  rising 
from  a  flat  iron  ring  supported  on  cast  iron  pillars  set 
in  the  solid  foundation  of  the  furnace.  Next  to  the  shell  is 
a  casing  of  ordinary  brickwork,  and  the  inside  lining  is  of 
refractory  bricks,  18  inches  thick.  They  are  both  built 
up  from  the  ring,  and  inside  the  shell,  so  that  the  whole  of 
this  part  of  the  furnace  is  independent  of  the  portion  below 
the  ring,  which  is  built  in  after  the  stack  is  complete.  The 
top  of  the  furnace  is  closed  by  the  charging  apparatus  and 


PIG  IRON  AND  ITS  MANUFACTURE.  75 

by  the  gallery  upon  which  the  materials  of  the  charge  are 
brought  previously  to  their  introduction  into  the  furnace. 


FIG.  11. — Modern  Blast  Furnace  (vertical  section). 

A,  Cup  and  cone.  E,  Hearth. 

B,  Charging  gallery.  F,  Twyers. 

c,  Gas  outlet.  G,  Horse  shoe  main. 

D,  Boshes.  II,  Dust  catcher. 

The  common  way  of  closing  the  furnace  top  is  by  means  of 
a  cup  and  cone  arrangement,  in  which  the  centre  of  the 
gallery  floor  is  dished  out  to  form  a  conical  charging 
hopper.  The  opening  from  this  hopper  into  the  throat  of 


76  IRON  AND  STEEL. 

the  furnace  is  closed  by  an  iron  cone  suspended  at  its  apex 
from  a  lever  arrangement  by  which  it  is  held  in  position, 
and  effectively  closes  the  mouth  of  the  hopper  cone,  except 
when  it  is  lowered  to  admit  a  charge.  The  gallery  floor  is 
lined  with  iron  plates. 

Below  the  charging  apparatus,  but  above  the  level  of 
the  charge,  there  is  a  wide  circular  opening  in  the  brick- 
work which  leads  outwards  to  a  wide  pipe,  the  "  down 
comer,"  that  passes  down  the  outside  of  the  furnace  to  an 
expanded  portion,  the  dust  catcher.  The  gallery  is  usually 
reached  from  the  ground  level  by  an  inclined  plane  furnished 
with  rails,  on  which  a  trolley  furnished  with  front  and  back 
wheels  of  different  diameters  and  a  horizontal  platform,  is 
made  to  ascend  and  descend.  The  trolley  is  counterpoised 
by  a  heavy  weight  suspended  from  a  steel  cable  passing 
over  a  pulley  at  the  top  of  the  plane ;  so  that  the  load  only 
has  to  be  lifted  to  the  furnace  top,  and  this  is  done  by  a 
steel  cable  worked  by  steam  power.  The  lower  terminus  of 
the  trolley  is  the  dock  on  which  the  materials  of  the  charge 
are  accumulated  in  iron  charging  barrows  that  can  be 
wheeled  straight  on  to  the  trolley  platform.  The  upper 
terminus  is  the  charging  gallery  on  to  which  the  barrows 
are  wheeled  when  the  trolley  reaches  it.  One  hoist  usually 
serves  several  furnaces,  the  galleries  of  which  are  connected 
together  by  bridge-ways.  Vertical  lifts  worked  by  hydraulic 
power  are  also  used  for  the  same  purpose. 

The  above  description  of  the  stack  or  shaft  of  the 
furnace  may  be  followed  by  that  of  the  hearth  and  com- 
bustion zone,  which  is  built  in  afterwards,  so  that  it  can  be 
taken  out  and  replaced  during  the  life  of  the  furnace 
without  interfering  with  the  shaft,  as  it  is  here  that  the 
principal  wear  and  tear  takes  place.  The  most  refractory 
materials  are  used  in  its  construction,  as  the  effects  of 
high  temperatures  and  the  corrosive  action  of  molten  matter 
must  be  counteracted  as  much  as  possible.  For  rapid 


PIG  IRON   AND   ITS   MANUFACTURE.  77 

working,  as  in  American  practice,  for  example,  water  blocks 
through  which  water  can  he  made  to  circulate  are  built  into 
the  parts  exposed  to  the  highest  temperature  to  prolong 
the  life  of  the  lining.  In  a  still  later  form  a  more  con- 
tinuous and  more  effective  circulation  of  water  is  obtained 
by  means  of  bosh  jackets,  which  encircle  the  furnace  just 
above  the  twyer  region.  No  leakage  can  take  place  into 
the  furnace,  as  the  jacket  pockets  are  only  24  inches  deep, 
and  the  blast  pressure  in  the  furnace  would  more  than 
counterbalance  this  depth  of  water  in  the  jacket.  The 
hearth  in  which  the  molten  matter  collects  is  circular 
in  plan  and  lined  with  shaped  bricks.  It  has  a  slightly 
concave  bottom,  built  in  the  form  of  an  inverted  arch  so  as 
to  prevent  bulging  upwards.  In  the  side  of  the  hearth  and 
close  to  the  bottom  is  a  rectangular  opening,  the  tap  hole, 
which  is  closed  with  clay  during  working ;  and  at  the  top  of 
the  hearth  are  a  number  of  circular  openings  through  which 
the  twyers  or  blast  pipes  are  inserted.  Below  these,  and 
usually  on  a  diameter  at  right  angles  to  the  tap  hole,  is  the 
opening  known  as  the  cinder  notch.  Above  the  hearth  the 
furnace  gradually  widens  until  it  reaches  its  maximum  at  the 
boshes.  The  outside  of  the  hearth  is  surrounded  by  a  moat 
filled  with  water  and  stones.  The  water  serves  to  keep  the 
lower  part  of  the  hearth  cool,  and  the  stones  prevent  the 
formation  of  a  solid  ring  of  metal  in  case  of  a  break  through. 
The  size  of  the  hearth  depends  generally  upon  the  size  of 
the  furnace,  and  is  usually  about  10  feet  in  diameter ;  but 
the  ratio  of  the  hearth  to  the  other  dimensions  varies  in 
different  furnaces.  Until  somewhat  recent  years  an  arch 
was  built  in  the  side  of  the  hearth,  the  lower  portion  of 
which  was  closed  by  the  "  damstone "  and  the  upper 
portion  by  the  "  tympstone."  These  were  faced  on  the 
outside  by  iron  plates,  and  the  cinder  notch,  a  semi-circular 
channel  in  the  top  of  the  dam-plate,  led  out  between  the 
upper  and  lower  plate.  In  this  arrangement  the  hearth  was 


IRON  AND   STEEL 


wider  near  the  arch,  and  the  space  behind  the  damstone 
was  known  as  the  fore  hearth.  But  this  seems  now  to 
have  entirely  disappeared,  and  the  hearth  of  the  modern 
furnace  has  a  uniform  cross  section. 

The  following  dimensions  of  a  recently-constructed  fur- 
nace are  given  :  height,  80  feet ;  diameter  at  boshes,  20  feet; 
diameter  of  hearth,  9  feet;  diameter  of  throat,  11  feet.  A 
vertical  section  through  such  a  furnace  is  shown  in  Fig.  11. 
The  ring  of  pillars  on  which  the  shaft  is  supported  also 
carries  the  horse-shoe  blast  main,  which  is  an  iron  pipe 

about  3  feet  in  diameter, 
and  lined  with  a  9-inch 
course  of  firebricks.  It 
has  therefore  an  internal 
diameter  of  18  inches, 
and  nearly  encircles  the 
furnace,  being  supported 
on  brackets  standing  out 
from  the  pillars.  Elbow 
tubes  or  goosenecks  pass 
downwards  from  it  to 

the  twyer  level,  there  to  be  connected  with  the  twyers.  The 
portion  of  the  twyer  that  enters  the  furnace  is  a  water  jacket 
(Fig.  12),  through  which  water  is  kept  circulating,  and  the 
pipe  from  the  gooseneck  through  which  the  blast  passes  is 
fitted  into  this.  A  view  of  the  interior  of  the  hearth  in  the 
region  of  the  end  of  the  twyer  can  be  obtained  through  a 
hole  in  the  elbow,  known  as  the  furnace  eye,  which  is  closed 
by  a  plate  of  mica,  or  by  a  plug,  when  not  in  use.  Each 
twyer  is  furnished  with  a  throttle  valve  by  which  the  blast 
can  be  cut  off  from  it  without  interfering  with  its  fellows. 
Six  twyers  are  used  for  a  furnace  of  the  dimensions  given 
above,  but  the  number  varies  in  different  furnaces.  The 
arrangement  at  the  bottom  of  the  furnace  is  shown  in 
Fig.  13. 


PIG  IEON  AND   ITS   MANUFACTURE. 


79 


FIG.  13. — Bottom  of  Blast  Furnace  showing  twyers  in  position. 

The  Blast. — Smelting  for  pig  iron  is  now  almost  entirely 
carried  out  with  hot  hlast,  which  was  introduced  by  Neilson 
in  1828,  and  it  is  only  high  grade  pig  iron  for  special 
purposes  that  is  now  smelted  with  cold  blast. 

The  method  of  heating  the  blast  has  undergone  many 


80  IRON  AND   STEEL. 

changes  since  Neilson's  time,  when  an  expanded  portion 
of  the  blast  main  was  surrounded  by  a  furnace  in  which 
solid  fuel  was  burnt,  and  the  blast  driven  through  it  before 
entering  the  furnace.  Various  forms  of  iron  pipe  stoves 
heated  with  solid  fuel  or  waste  gas  have  been  used,  but 
have  now  almost  entirely  given  place  to  stoves  of  the 
regenerative  principle,  which  are  much  more  suitable  for 
using  the  blast  furnace  gas  itself  for  heating  the  blast. 
One  of  the  earliest  stoves  of  this  pattern  was  designed  and 
constructed  by  Cowper  in  1860  to  burn  solid  fuel ;  but 
shortly  after  he  proposed  to  use  "  waste  "  gas,  and  the 
later  ones  are  all  modifications  or  extensions  of  Cowper 's 
original  stove.  The  principle  of  regeneration  demands  at 
least  two  stoves,  and  each  stove  consists  of  a  huge  chamber, 
the  interior  of  which  is  built  in  with  firebrick  intersected 
by  flues,  in  which  combustible  gas  is  burnt  to  develop  heat, 
which  is  absorbed  by  the  brickwork  and  re-absorbed  by 
the  air  when  the  chamber  is  put  in  the  path  of  the  blast 
on  its  passage  from  the  blowing  engine  to  the  furnace. 
Thus  the  chambers  are  alternately  heating  the  blast  and 
being  re-heated  by  the  burning  gas ;  hence  the  necessity 
for  at  least  two  stoves. 

The  Modern  Blast  Stove  is  almost  as  large  as  the  furnace 
it  serves.  It  is  circular  in  cross-section,  and  consists  of  a 
gas-tight  shell  formed  of  curved  iron  plates.  In  some 
cases  it  is  from  70  to  80  feet  in  height  and  25  to  30 
feet  in  diameter.  The  inside  of  the  shell  is  lined  with  fire- 
bricks, and  the  interior  is  built  in  with  a  mass  of  brickwork 
through  which  run  the  necessary  flues  and  passages  for 
carrying  on  the  combustion  of  the  furnace  gas,  and  for 
exposing  a  very  large  total  heating  surface  to  the  air 
brought  into  contact  with  it  when  the  blast  is  passing 
through.  It  is  estimated  that  five  square  feet  of  heating 
surface  are  necessary  for  every  cubic  foot  of  air.  The 
passages  should  therefore  be  arranged  so  as  to  expose  as 


PIG  IEON  AND   ITS  MANUFACTURE. 


si 


large  a  surface  as  possible,  compared  with  their  cross-section, 
as  is  consistent  with  the  other  conditions  of  working.  It  is 
easy  to  see  that  the  smaller  the  cross-section  of  the  passages 
the  greater  will  be  the  total  heating  surface,  but  also  the 


FIG.  14. — Cowper's  Hot-blast  Stove. 

A,  Man-hole.  F,  Gas  culvert. 

B,  Combustion  flue.  G,  Gas  valve. 
c,  Honeycomb  brickwork.                  H,  Air  inlet. 

D,  Chimney  valve.  I,  Hot-blast  main. 

E,  Culvert  to  chimney.  J,  Hot-blast  valve. 

greater  the  frictional  resistance  to  the  passage  of  gas 
through  them.  Other  conditions,  such  as  total  capacity, 
rate  of  flow,  and  facilities  for  cleaning,  determine  the  size 
of  the  stove  and  its  general  arrangement.  In  the  modern 
Cowper  stove,  the  general  construction  of  which  is  shown 
in  Fig.  14,  the  regenerative  part  presents  somewhat 
i.s.  G 


82  IEON  AND   STEEL. 

the  appearance  of  a  honeycomb  in  cross-section.  This 
honeycomb  structure  is  built  up  from  an  iron  grid  which  is 
supported  on  columns  just  above  the  bottom.  It  fills  more 
than  two-thirds  of  the  cross-section,  and  extends  nearly 
to  the  top  of  the  stove.  It  is  built  of  shaped  bricks,  and  the 
walls  dividing  the  passages  are  about  two  inches  thick  ;  but 
the  passages  themselves  are  about  six  inches  wide,  and 
hexagonal  in  cross-section.  The  combustion  flue,  which  is 
a  lens-shaped  passage  with  thick  walls,  extends  from  below 
the  grid  up  to  the  level  of  the  regenerative  brickwork.  The 
lower  portion  of  this  flue  is  divided  into  several  narrower 
channels  by  vertical  partition  walls.  The  gas  and  air 
inlets  are  at  the  bottom  of  the  flue  just  below  these  partitions, 
and  the  hot  blast  outlet  just  above  them.  The  outlet  to 
the  chimney  communicates  with  the  space  under  the  grid, 
and  leads  into  an  underground  culvert  connected  with  the 
main  stack.  Eeference  to  Fig.  14  will  make  the  general 
arrangement  clear.  The  cold  blast  inlet  is  not  shown. 

For  working  the  stove  combustible  furnace  gas  is  admitted 
to  the  combustion  flue  through  the  gas  inlet  valve,  while 
sufficient  air  to  burn  it  completely  is  drawn  through  the 
air  inlet  valve  just  above.  The  flue  being  hot,  the  gas  fires 
immediately,  and  the  current  of  burning  gas  is  broken  up 
into  sheets  in  passing  through  the  spaces  between  the 
partition  walls.  This  is  said  to  ensure  more  perfect  com- 
bustion of  the  gas.  The  flame  and  products  of  combustion 
then  pass  up  the  flue  and  down  through  the  hexagonal 
passages  in  the  honeycomb  structure;  and  in  doing  so 
leave  behind  in  the  brickwork  practically  the  whole  of  the 
heat  developed  by  the  combustion  of  the  gas,  for  the  burnt 
gas  leaves  the  stove  at  much  the  same  temperature  as  the 
raw  gas  entered  it ;  but  strictly,  the  heat  carried  off  by  the 
nitrogen  of  the  air  used  to  burn  the  gas  would  have  to  be 
considered.  When  the  temperature  of  the  stove  has  been 
sufficiently  raised,  the  gas  and  air  supply  is  cut  off,  the 


PIG  IEON  AND   ITS  MANUFACTURE. 


chimney  valve  closed,  and  the  cold  blast  turned  on.  The 
cold  air  passes  into  the  space  under  the  grid,  through  the 
regenerator  passages,  down  the  combustion  flue,  and 
through  the  hot-blast  outlet  into  the  hot-blast  main,  by 
which  it  is  conveyed  direct  to  the  furnace.  The  blast  is 
driven  through  the  hot  stove  until  the  brickwork  is 
sufficiently  cooled  down,  when  it  is  cut  off  and  the  gas  and 
air  supply  turned  on  again.  From  this  it  is  clear  that  two 

stoves  at  least  must  be 
in  use,  one  for  heating 
the  blast  while  the  other 
is  itself  being  heated. 
The  temperature  of  the 
blast  often  reaches  800° 
C.,  and  a  large  quantity 
of  heat  must  be  absorbed 
by  the  air  to  obtain  this 
result.  The  rush  of  air 
from  the  cold  blast  main 
is  immediately  slowed 
down  by  the  larger  sec- 
tional area  over  which  it 
is  spread,  and  the  slower 
current  has  a  long  path 
to  travel  through,  so  that 
time  is  given  for  suffi- 
the  air  to  raise  it  to  the 


FIG.  15. — Blowing  Cylinder. 

V,  Air  valves  for  down-stroke. 
V,  Air  valves  for  up-stroke. 
V",  Valves  to  blast  main. 


cient   heat  to  be   absorbed   by 
proper  temperature. 

The  blast  is  furnished  by  blowing  engines  of  the  cylinder 
type,  and  as  enormous  quantities  of  air  must  be  set  in 
motion,  they  are  very  large.  They  form  a  very  important 
part  of  blast  furnace  equipment,  as  from  five  to  six  tons  of 
air  must  be  driven  through  the  furnace  for  every  ton  of  pig 
iron  produced.  A  cubic  foot  of  air  weighs  about  0*0761b., 
so  that  a  ton  of  air  would  have  a  volume  of  about  30,000 

G  2 


84  IRON  AND   STEEL. 

cubic  feet.  Blowing  engines  of  the  beam  type  have  not  yet 
disappeared,  but  direct-acting  engines  in  which  the  blowing 
cylinder  and  the  steam  cylinder  are  placed  one  above  the 
other  are  now  largely  used.  The  two  pistons  are  connected 
by  the  same  rod,  and  move  up  and  down  the  cylinders  at 
the  same  time.  Double-cylinder  engines  for  using  both 
high  and  low  pressure  steam  are  the  most  economical  when 
steam  is  to  furnish  the  motive  power;  but  gas  engines 
burning  blast  furnace  gas  direct  will  no  doubt  furnish  the 
whole  of  the  blowing  power  in  the  future,  and  are 
extensively  used  in  some  works  at  the  present  time. 

The  size  of  the  blowing  cylinders  varies  somewhat  with 
the  work  to  be  done.  Some  of  them  are  upwards  of  ten 
feet  in  diameter  and  of  the  same  length,  with  a  piston  area 
of  about  100  square  feet.  Such  a  cylinder  will  deliver 
upwards  of  50,000  cubic  feet  of  air  per  minute.  An  idea  of 
the  general  construction  of  a  blowing  cylinder  is  given  by 
Fig.  15. 

In  this  country  it  is  the  general  practice  to  use  a  powerful 
engine  for  supplying  the  blast  to  several  furnaces  ;  but  in 
America  the  furnaces  are  more  self-contained,  the  blast 
being  supplied  direct  to  a  single  furnace,  so  that  smaller 
engines  are  required.  This  is  no  doubt  due  to  the  greater 
pressure  required  for  the  very  rapid  driving  common  to  the 
Western  continent. 

The  blast  pressure  used  in  different  furnaces  varies 
considerably  according  to  the  kind  of  furnace  and  the  work 
to  be  done  in  it.  Thus  a  charcoal  furnace  may  be  driven 
with  a  pressure  of  less  than  lib.  per  square  inch,  while  a 
rapidly  driven  American  furnace  may  require  a  pressure  of 
151b.  per  square  inch.  In  general  practice  it  varies  from 
31b.  to  7lb.  The  height  of  the  furnace,  the  density  of  the 
materials  in  the  charge,  and  the  rate  of  working  have  all  to 
be  taken  into  consideration  ;  but  sufficient  air  must  be 
driven  in  to  keep  up  a  continuous  stream  through  the 


PIG  IRON  AND  ITS  MANUFACTURE. 


85 


furnace.  The  greater  the  pressure  in  a  given  cylinder  the 
greater  will  be  the  weight  of  air  supplied  in  unit  time. 
Considerable  fluctuation  of  the  blast  pressure  takes  place 
during  actual  working,  but  it  is  fairly  under  control. 
Mercury  pressure  gauges  are  placed  near  the  blowing 
cylinder,  and  also  near  the  hot-blast  main. 


FIG.  16.— A  Modern  Blast  Furnace  Plant. 


Fig.  16  gives  an  idea  of  the  general  arrangements  of  the 
blast  furnace  plant  in  a  modern  ironworks. 

The  Blast  Furnace  Changes. — The  charge  passing  through 
the  hopper  at  the  top  of  a  blast  furnace  consists  of  a 
properly  proportioned  mixture  of  ore,  flux,  and  fuel,  which 
is  so  arranged  that  the  gangue  of  the  ore,  together  with  the 
ash  of  the  fuel,  is  converted  into  slag  by  the  flux,  while  the 
iron  is  separated  as  metal  by  the  reducing  action  of  gas 
furnished  by  the  incomplete  combustion  of  the  fuel.  The 
charge  sinks  down  the  furnace  at  the  rate  of  about  three 


86  IEON  AND  STEEL. 

feet  per  hour.  This,  however,  depends  upon  the  rate  at 
which  the  furnace  is  being  driven.  This  descending 
stream  of  solid  matter  is  penetrated  by  a  current  of  gas 
that  passes  upwards  at  the  rate  of  about  three  feet  per 
second,  also  depending  on  the  working  of  the  furnace. 

The  zone  of  combustion,  as  that  part  of  the  furnace  near 
to  and  just  above  the  twyers  is  called,  is  the  region  in 
which  the  highest  temperature  is  generated,  and  no  solid 
matter  remains  long  in  the  solid  state  in  this  region  except 
the  coke,  which  is  constantly  falling  into  it  from  the 
charge  above.  It  is,  in  fact,  a  solid  bed  of  white-hot 
carbon,  through  which  the  molten  metal  and  slag  trickle 
into  the  hearth  below.  The  blast  of  hot  air  comes  into 
contact  with  this  highly-heated  fuel,  and  the  carbon  is 
practically  burnt  at  once  to  carbon  monoxide,  CO,  instead 
of  being  first  completely  burnt  to  carbon  dioxide,  C02,  as 
would  be  the  case  with  cold  blast  and  a  fuel  bed  at  a  lower 
temperature.  The  current  of  air  is  thus  robbed  of  its 
oxygen  low  down  in  the  furnace,  and  passes  upwards, 
carrying  the  carbon  monoxide  with  it ;  this  gas  is  thus 
brought  into  contact  with  the  heated  oxide  of  iron  in  the 
charge,  and  reduces  it  to  the  metallic  state,  thus  :— 

Fe203  +  SCO  =  2Fe  +  SCO,, 

but  the  carbon  monoxide  must  be  in  considerable  excess 
or  the  oxide  of  iron  is  only  partially  reduced,  thus  :— 

Fe203  +  CO  =  2FeO  +  C02. 

Also,  if  carbon  dioxide  accumulates  in  large  excess  in  the 
furnace  gas,  the  reduced  iron  is  oxidised  again,  as  follows : 

2Fe  +  3C02  =  Fe203  +  3CO. 

This  makes  it  clear  that  the  furnace  gas  must  contain  a 
large  proportion  of  carbon  monoxide,  if  the  oxide  of  iron  is 
to  be  properly  reduced. 


PIG  IEON   AND  ITS  MANUFACTUKE.  87 

Oxide  of  iron  is  also  reduced  at  even  a  low  red  heat  by 
solid  carbon;  but  this  reaction  is  probably  not  an 
important  one  in  blast-furnace  changes.  Carbon  dioxide  is 
formed  by  this  reaction,  thus  :— 

2Fe203  +  30  =  4Fe  +  3C02. 

Under  proper  conditions  the  metal  is  completely  reduced 
in  that  part  of  the  furnace  where  the  temperature  reaches 
a  red  heat.  The  iron  thus  produced  is  in  a  spongy  state, 
and  is  able  to  abstract  carbon  from  the  carbon  monoxide, 
and  from  the  fuel,  with  which  it  is  in  contact.  The  re- 
action may  be  expressed  in  a  general  way  by  the  equation— 

^Fe  +  2CO  =  Fe.C  +  C02. 

The  limestone  flux  is  decomposed  at  a  red  heat  into  lime 
and  carbon  dioxide,  and  the  latter  is  largely  converted  into 
carbon  monoxide  in  contact  with  the  red  hot  coke,  thus 
preventing  the  accumulation  of  carbon  dioxide  in  the 
reducing  zone.  This  is  shown  by  the  equation : — 

CaC03  +  C  =  CaO  +  2CO. 

Lower  down  the  furnace,  where  the  temperature  is  much 
higher,  silica  is  reduced  by  solid  carbon  in  the  presence  of 
iron,  and  the  silicon  passes  into  the  metal.  Phosphorus, 
manganese,  and  sulphur  are  also  reduced  from  their 
compounds,  and  pass  into  the  metal,  which  is  now  in  a 
perfectly  fluid  state,  and  filters  through  the  coke  bed  into 
the  hearth  below.  The  lime  unites  with  the  remaining 
earthy  matter  of  the  gangue  and  the  ash  of  the  fuel  to 
form  the  liquid  slag,  which  runs  down  into  the  hearth,  and 
floats  on  top  of  the  molten  metal.  The  reduction  of  these 
oxides  is  a  simple  matter  when  the  furnace  conditions  are 
favourable,  as  they  are  decomposed  by  carbon  at  a  white 
heat  with  formation  of  carbon  monoxide,  and  being  set  free 


88  IKON  AND  STEEL. 

in  the  presence  of  the  metal,  pass  into  it.     The  reduction 
of  phosphoric  oxide  and  silica  is  typical  :— 

PA  +  5C  =  2P  +  5CO. 
Si02  +  2C  =  Si  -f  2CO. 

The  impurities  that  find  their  way  into  the  metal  all 
come  from  the  gangue  and  the  fuel.  The  proportions, 
however,  that  pass  into  the  metal  depend  very  largely 
upon  the  temperature  of  the  furnace  and  the  composition 
of  the  slag. 

The  Furnace  Charge. — As  already  indicated,  the  gangue 
of  the  ore  and  the  ash  of  the  fuel  are  for  the  most  part 
converted  into  fusible  slag,  and  since  the  composition  of 
this  slag  must  be  kept  within  somewhat  narrow  limits  the 
proportion  between  the  ore  and  the  flux  must  be  carefully 
arranged.  The  nature  of  the  gangue  must  also  be 
considered.  Limestone  is  the  common  flux,  but  if  the  chief 
ore  is  siliceous,  then  material  containing  alumina  must  be 
added,  and  clay  is  sometimes  used  for  this  purpose.  But 
it  is  preferable  to  use  iron-bearing  materials  when  they  can 
be  obtained,  and  Irish  bauxite,  which  is  rich  in  alumina 
and  ferric  oxide,  is  very  useful.  Sometimes  a  slag  rich  in 
alumina  is  added.  When  a  variety  of  ores  is  at  hand  it 
is  often  possible  to  prepare  an  ore  mixture  containing 
sufficient  alumina  to  flux  properly  with  the  added  lime  ;  and 
at  times  a  mixture  can  be  made  "  self-going,"  that  is,  to 
require  no  added  limestone. 

The  composition  of  the  main  bulk  of  the  slag  formed  in 
hot-blast  working  may  be  represented  by  the  formula — 

6(2CaO.  Si02)  +  2  Al203-3Si02 

6(112  +  60)  204  +  180 

from  which  the  percentage  composition  is  readily  calculated, 
and  gives — 


PIG  IEON  AND  ITS  MANUFACTURE.  89 

Silica,  Si02 38'1 

Alumina,  A1203 14'7 

Lime,  CaO 47'2 

100-0 

This  forms  about  85  per  cent,  of  the  average  slag,  the 
remaining  15  per  cent,  being  made  up  of  the  silicates  of 
other  oxides,  such  as  ferrous  oxide,  FeO,  manganous  oxide, 
MnO,  magnesia,  MgO,  and  the  alkalies.  Phosphates  and 
sulphides,  too,  are  often  present. 

Strictly  speaking,  this  slag  is  a  normal  double  silicate 
of  lime  and  alumina  (monosilicate),  but  it  is  usually  described 
as  basic  in  character  on  account  of  the  large  percentage  of 
bases  it  contains.  It  is  not  readily  fusible,  and  requires 
the  high  temperature  of  the  hot  blast  to  render  it  perfectly 
fluid.  Dolomite  is  sometimes  used  in  the  Cleveland  district 
in  place  of  lime,  although  it  thickens  the  slag,  as  it  is 
supposed  to  favour  the  passage  of  sulphur  into  the  slag. 

In  cold-blast  working  the  slag  usually  aimed  at  has  the 
composition  expressed  by  the  formula — 

3(CaO.Si02)  +  Al203.3Si02 

3(56  +  60)  102  +  180 

This  gives — 

Silica,  Si02 57'2 

Alumina,  A1203 16'2 

Lime,  CaO  .  .  26'6 

100-0 

It  is  the  acid  double  silicate  (bisilicate),  and  is  more 
fusible  than  the  one  given  above ;  it  forms  the  main  bulk 
of  the  slag. 

In  certain  conditions  of  the  furnace,  with  regard  to  the 
composition  of  the  charge  and  the  general  working,  a  very 
fluid  slag,  called  a  ''scouring"  slag,  is  produced.  This 


90 


IRON  AND  STEEL. 


contains  an  unusual  amount  of  ferrous  oxide,  and  exerts  a 
corrosive  action  on  the  furnace  lining.  Such  a  slag  is 
produced  when  a  large  proportion  of  cinder  is  used  in  the 
charge. 

Blast  furnace  slags  vary  considerably  in  appearance. 
Some  are  dull  and  stony  looking,  and  others  are  glassy  in 
character.  This  depends  upon  the  composition  of  the  slag 
and  its  rate  of  cooling.  Eapid  cooling  tends  to  the  for- 
mation of  a  glass.  Slags  vary  in  colour  from  brownish 
yellow  to  black,  passing  through  various  shades  of  green 
and  blue.  Parts  of  the  same  piece  sometimes  differ  in 
colour  and  character. 

Most  blast  furnace  managers  have  their  own  methods  of 
making  up  the  charge ;  but  this  presents  no  difficulty  to 
the  experienced  man  when  the  composition  of  the  materials 
at  hand  is  known.  He  has  to  consider  the  grade  of  pig  to 
be  produced  and  use  his  knowledge  of  the  general  working 
of  the  furnaces  under  his  control.  Tables  and  curves,  such 
as  Balling's,  are  used,  but  only  general  outlines  can  be 
given.  The  following  are  typical  :— 


(1)   Scotch  Furnace  using  coal  (Sexton) — 


INTAKE. 


Ore  mixture 
Limestone 
Coal  . 
Blast 


2-50  tons. 

Pig  iron     . 

0-50     „ 

Slag  .         . 

1-75     „ 

Furnace  gas 

6-00     „ 

10-75  tons. 

OUTPUT. 


(2)  Cleveland  Furnace  using  coke  (Turner)— 


INTAKE. 


Ore  mixture 
Limestone  . 
Coke  . 
Blast  . 


2-4  tons. 

Pig  iron 

0-6     „ 

Slag    .         . 

i-o    „ 

Furnace  gas 

5-0     „ 

9-0  tons. 

OUTPUT. 


1-00  tons. 
1-50     ,, 

8-25     „ 

10'7f>  tons. 


!•()  tons. 
1-5     „ 
6-5 


9-0  tons. 


PIG  IEON  AND  ITS  MANUFACTURE. 


91 


The  average  composition  of  the  furnace  gas  from  a  coke 
furnace  may  be  taken  as  follows  :— 


Carbon  monoxide,  CO 
Hydrogen,  H2 
Carbon  dioxide,  C02    . 
Nitrogen,  N2 


29  I 
3  j- 

9  ) 
59  f 

100 


Combustible. 

Non- 
combustible. 


In  the  ordinary  method  of  charging,  the  materials  in 
the  proportions  for  the  charge  are  raised  to  the  gallery  of 
the  furnace  in  iron  bar- 
rows, and  tipped  into  the 
cup  by  the  "fillers,"  as 
the  men  at  the  top  are 
called.  The  cone  is  then 
released,  and  sinks  under 
the  weight  of  the  charge, 
which  then  slides  down 
its  inclined  sides  into  the 
furnace.  When  relieved 
of  the  charge  the  cone  is 
raised  again  by  the 
counterpoise  weight  at 
the  other  end  of  the  lever,  and  the  cup  closed.  The  proper 
distribution  of  the  charge  in  the  furnace  is  most  impor- 
tant, and  depends  upon  the  diameter  of  the  aperture  in 
the  cup,  and  the  slope  of  the  sides  of  the  cone,  both  of  which 
are  carefully  regulated.  In  the  form  of  apparatus  shown 
in  Fig.  17,  the  motion  of  the  lever  from  which  the  cone  A 
is  suspended  is  governed  by  means  of  a  cylinder  and  plunger 
B,  as  well  as  by  the  counterpoise  W.  The  cylinder  is  full 
of  water,  and  when  the  tap  in  the  connecting  pipe  is  closed 
the  plunger  is  held  in  position,  but  when  it  is  open  the 
plunger  can  move  either  up  or  down.  The  motion  of  the 
cone  is,  therefore,  well  under  control.  The  bolt  rod  C  is 


FIG.  17. 


92  IEON  AND   STEEL. 

also  used  while  the  charge  is  being  thrown  in.  The  level 
of  the  charge  is  not  allowed  to  rise  above  the  gas  outlet  D, 
and  is  determined  by  pushing  an  iron  rod  through  apertures 
in  the  gallery  floor  E  into  the  throat  of  the  furnace.  The 
motion  of  the  cone  up  and  down  is  made  as  rapid  as  possible 
so  as  to  prevent  the  escape  of  the  furnace  gas. 

Variations  in  the  Air. — The  composition  and  general 
character  of  the  various  ores,  limestone,  and  coke  have  been 
described  in  Chapter  II.,  and  it  remains  to  describe  the 
general  properties  of  the  air  used  for  the  blast.  It  is  quite 
evident  from  the  enormous  quantity  used  that  variations  in 
its  composition  must  have  considerable  influence  on  the 
working  of  the  furnace.  The  variable  constituent  which 
exerts  the  greatest  influence  is  water  vapour.  It  has  long 
been  known  that  an  increase  or  a  decrease  in  the  quantity 
of  water  vapour  driven  into  the  furnace  has  a  decided 
influence  on  its  working.  If,  then,  a  perfectly  uniform  blast 
is  to  be  obtained  the  percentage  of  water  vapour  in  it 
must  be  kept  constant.  It  would  be  impossible  to  com- 
pletely remove  the  moisture  from  so  large  a  bulk  of  air  at 
anything  like  a  reasonable  cost;  so  that  all  that  can  be 
done  is  to  reduce  the  quantity,  and  produce  a  blast  that  shall 
be  of  uniform  composition  from  time  to  time.  J.  Gayley, 
an  American  authority,  states  that  a  saving  of  coke  and  an 
increase  in  the  output  can  be  effected  by  causing  the  air  to 
pass  through  refrigerators  before  it  enters  the  blowing 
cylinders.  The  air  is  thus  cooled  down  below  its  saturation 
point,  and  the  excess  water  vapour  condensed  and  deposited 
in  the  refrigerators.  In  this  way  it  is  possible  to  reduce 
the  quantity  of  moisture  in  the  dried  air  to  about  1  grain 
per  cubic  foot.  It  is  well  known  that  the  quantity  of  water 
vapour  in  the  air  may  vary  from  day  to  day,  and  that  it  is 
less  in  the  winter  than  in  the  summer.  In  this  country 
the  average  quantity  is  said  to  be  5'5  grains  per  cubic  foot 
for  summer  and  3*5  grains  for  winter.  More  heat  is  carried 


PIG  IKON  AND   ITS  MANUFACTUEE.  93 

away  in  the  gases  when  moist  air  is  used  than  when  it  is 
dried  ;  so  that  the  furnace  top  is  hotter,  and  there  is  more 
liability  to  the  reduction  of  carbon  dioxide  to  the  monoxide, 
where  it  is  not  wanted,  with  a  consequent  increase  of  the 
coke  consumption.  This  is  borne  out  by  the  fact  that  the 
fuel  consumption  is  less  in  the  winter  than  in  the  summer. 

W.  Kichards  is  of  opinion  that  it  is  preferable  to  dry  the 
air  than  to  try  to  regulate  the  temperature  of  the  blast 
according  to  atmospheric  variations. 

The  principal  action  of  the  water  vapour  in  the  furnace 
seems  to  be  to  reduce  the  temperature  of  the  coke  bed  by 
causing  the  change  (C  +  H20  :  :  CO  -f  H2),  which  is 
endothermic  in  character,  and  results  in  the  absorption  of 
heat.  This  extends  the  zone  of  combustion  upwards  and 
tends  to  a  hotter  top,  as  stated  by  Gayley.  Thus,  the  more 
moisture  there  is  in  the  air,  the  hotter  must  be  the  blast  to 
preserve  uniform  working.  Some  of  the  hydrogen  set  free 
no  doubt  takes  part  in  the  reduction  of  the  metal,  but  free 
hydrogen  is  nearly  always  found  in  the  furnace  gas.  There 
has  been  much  discussion  as  to  the  general  utility  of  drying 
the  blast,  but,  like  other  modifications  in  blast  furnace 
practice,  it  will  have  to  pass  through  the  test  of  experience. 

Hot  Blast. — When  Neilson  introduced  his  method  of 
heating  the  blast  in  1828  it  was  thought  that  there  would 
be  little  or  no  saving  of  fuel,  as  it  was  difficult  to  understand 
why  the  burning  of  a  given  weight  of  fuel  in  the  furnace 
should  not  give  as  good  a  result  as  when  part  of  it  was 
burnt  outside  to  heat  the  blast.  This  was  probably  due  to 
the  then  imperfect  knowledge  of  the  furnace  changes.  But 
in  practice  it  was  soon  found  that  a  great  economy  was 
effected.  According  to  Prof.  Turner  a  consumption  of 
upwards  of  8  tons  of  coal  per  ton  of  pig  iron  was 
reduced  to  about  5  tons  by  heating  the  blast  to  170°  C., 
and  a  still  further  reduction  to  about  2J  tons  when  the  blast 
was  heated  to  300°  C.  This  was  in  1833,  so  that  the 


94  IKON   AND   STEEL. 

economy  of  the  system  was  soon  proved ;  and,  although  the 
consumption  of  fuel  per  ton  of  pig  was  greater  in  Scotland 
than  in  other  parts  of  the  country,  the  use  of  hot  blast 
grew  rapidly.  In  South  Wales  it  enabled  anthracite  to  be 
used  in  the  furnace ;  and  in  Staffordshire  it  initiated  the 
smelting  for  "cinder"  pig  as  distinguished  from  "all 
mine  "  pig. 

In  considering  the  theory  of  the  hot  blast  it  should  be 
borne  in  mind  that  there  are  two  oxides  of  carbon,  and  that 
where  there  is  a  sufficient  quantity  of  air  the  tendency  is 
for  the  carbon  to  burn  completely  to  the  higher  oxide, 
C02,  while  with  a  limited  quantity  of  air  the  lower  oxide 
CO  is  formed,  provided  the  temperature  generated  is  high 
enough  to  allow  of  the  change — 

C  +  C02  =  2CO, 

and  this  is  probably  the  origin  of  the  carbon  monoxide  in  a 
furnace  working  with  cold  blast. 

Now  there  is  a  temperature  range  within  which  carbon 
dioxide  is  decomposed  into  carbon  monoxide  and  oxygen— 

C02  -  CO  +  0, 

and  when  the  temperature  of  the  zone  of  combustion  is 
well  within  this  range  very  little  carbon  dioxide  is  formed  ; 
or,  what  amounts  to  the  same  thing,  is  decomposed  as  fast 
as  it  is  formed.  Therefore  the  principal  product  of  the 
combustion  is  carbon  monoxide.  Now,  it  is  perfectly  clear 
that  by  blowing  hot  air  into  the  zone  of  combustion  its 
temperature  would  be  raised  in  proportion  to  the  temperature 
of  the  incoming  air,  as  the  heat  it  brought  in  would  be 
added  to  that  generated  by  the  combustion  induced  by  its 
oxygen.  It  is,  therefore,  readily  understood  that  the 
temperature  might  be  bigh  enough  to  prevent  the  formation 
of  the  higher  oxide,  except  in  small  quantity.  So  that  in 
considering  the  extra  efficiency  and  economy  of  the  hot 


PIG  IRON  AND  ITS  MANUFACTUKE.  9,3 

blast  it  must  be  borne  in  mind  that  the  heat  carried  into 
the  furnace  by  the  blast  causes  an  increase  in  the 
temperature  of  combustion,  with  more  rapid  melting  of 
metal  and  slag.  That  the  zone  of  combustion  is  more 
localised,  as  carbon  monoxide  is  practically  formed  at  once 
instead  of  carbon  dioxide  being  first  formed  and  then  having 
to  pass  some  distance  up  the  furnace  before  its  conversion 
into  the  monoxide.  Also,  that  as  a  smaller  quantity  of  air 
is  required  with  the  hot  blast  to  generate  the  same  tem- 
perature, the  consumption  of  coke  is  reduced,  and  therefore 
the  amount  of  ash  to  be  fluxed  off  is  less.  Thus  the  top  of 
the  furnace  is  cooler,  the  burden  is  heavier,  the  working  is 
more  rapid,  and  the  yield  is  increased. 

The  thermal  efficiency  of  the  blast  furnace  has  formed 
the  subject  of  important  papers  by  Mr.  W.  J.  Foster,1  who 
is  of  opinion  that  the  problem  is  a  complicated  one,  to 
which  the  manager  who  wishes  to  get  the  best  out  of 
his  furnaces  must  give  careful  consideiation.  For  a  full 
determination  it  would  be  necessary  to  know  the  specific 
heats  of  all  the  matter  in  the  system  and  their  variations 
with  the  changes  of  temperature  in  the  furnace.  He  draws 
attention  to  the  influence  of  heat  on  compounds,  such  as 
water,  which  are  dissociated  at  high  temperatures  with 
absorption  of  much  heat,  and  concludes  that  part  of  this 
heat  is  absorbed  and  rendered  latent  at  temperatures  below 
the  dissociation  point.  Thus  the  specific  heat  of  water 
vapour  would  be  largely  increased  at  the  temperature  of  the 
furnace,  and  further  heating  of  the  blast  would  not  be 
equivalent  to  the  removal  of  a  corresponding  quantity  of 
water  vapour  calculated  according  to  its  ordinary  specific 
heat.  He  also  discusses  the  endothermic  changes  mentioned 
above,  and  considers  the  whole  of  the  matter  concerned  in 
the  working  of  the  furnace. 

1  Journal  of  the  Iron  and  Steel  Institute,  1904,  and  Proceedings  of 
the  Staffordshire  Iron  and  Steel  Institute,  1907. 


96  IRON  AND   STEEL. 

Temperature  and  Pressure  of  the  blast  require  careful 
regulation  for  uniform  working.  Now  the  temperature  of 
the  air  entering  the  furnace  depends  upon  the  manipula- 
tion of  the  hot-blast  stoves,  and  when  thermal  measure- 
ments are  taken  they  are  made  in  some  part  of  the  hot- 
blast  main  near  the  furnace.  A  recording  pyrometer 
affords  the  best  means  of  dealing  with  this  problem,  for 
it  may  be  made  to  trace  a  curve  that  will  show  the 
variations  in  the  temperature  of  the  blast  from  time  to 
time.  Sometimes  thin  rods  of  alloys  of  known  melting 
points  are  used.  These  are  pushed  through  a  special  aper- 
ture in  the  hot-blast  main  so  as  to  be  in  contact  with  the 
hot  air,  and  its  temperature  is  then  known  to  lie  between 
the  melting  points  of  two  rods,  one  of  which  melts  while 
the  other  remains  solid. 

The  pressure  is  recorded  by  pressure  gauges  attached  to 
the  main,  but  sometimes  the  twyers  get  stopped  up  so  that 
little  or  no  blast  passes  through  them,  and  this  causes 
irregular  working.  A  very  simple  arrangement  for  indi- 
cating when  a  twyer  is  not  blowing  may  be  described  as 
follows  :  a  small  aperture  in  the  blast  main  just  above  the 
goose  neck  is  connected  by  a  pipe  with  one  limb  of  a  U  tube 
pressure  gauge,  and  a  similar  aperture  in  the  goose  neck 
itself  just  below  the  throttle  valve  is  connected  with  the 
other  limb  of  the  gauge.  The  friction  of  the  parts  of  the 
valve  and  the  sides  of  the  tube  as  the  air  rushes  through 
the  goose  neck  on  its  way  to  the  twyer  reduces  the  pressure 
from  what  it  is  in  the  blast  main  above.  This  causes  the 
liquid  in  the  limb  of  the  gauge  connected  with  the  goose 
neck  to  be  higher  than  it  is  in  the  limb  connected  with  the 
main,  for  the  lower  pressure  in  the  one  limb  requires  a 
longer  column  of  liquid  to  help  to  balance  the  higher  pres- 
sure in  the  other  limb.  This  is  a  clear  indication  that  the 
twyer  is  working.  If,  however,  the  twyer  gets  stopped 
from  any  cause,  the  liquid  sinks,  and  the  gauge  reads  level 


PIG  IRON  AND   ITS  MANUFACTURE.  97 

in  both  limbs,  for  with  no  friction  the  pressure  is  the  same 
on  both  sides. 

The  pressure  of  the  blast  varies  very  considerably  in 
general  practice.  It  may  be  as  low  as  2  Ibs.  per  square 
inch  in  a  slowly-driven  furnace,  or  as  high  as  15  Ibs.  per 
square  inch  in  a  rapidly-driven  American  furnace.  But 
there  is  always  considerable  leakage  between  the  blowing 
cylinder  and  the  twyer,  and  the  greater  the  pressure  the 
greater  the  loss.  Thus  with  a  pressure  of  2  Ibs.  the  loss  is 
only  2  per  cent.,  but  with  a  pressure  of  10  Ibs.  it  may 
amount  to  as  much  as  25  per  cent.,  the  greater  part  of 
which  is  lost  in  the  stoves. 

Equalisers. — In  ordinary  hot  blast  practice  with  regene- 
rative stoves  the  blast  is  turned  on  and  off  a  given  stove  at 
regular  intervals.  During  the  "  on  "  interval  the  blast  is 
taking  heat  from  the  brickwork  of  the  stove  and  cooling  it 
down,  so  that  at  the  end  of  the  interval  both  the  stove  and 
the  blast  it  is  heating  are  at  a  lower  temperature  than  at 
the  beginning.  This  fall  in  the  temperature  of  the  blast,  if 
it  is  at  all  considerable,  must  interfere  with  the  uniform 
working  of  the  furnace.  In  order  to  remedy  this  Messrs. 
Gjers  and  Harrison  suggested  the  use  of  a  smaller  stove, 
which  they  called  an  equaliser,  between  the  heating  stove 
and  the  hot  blast  main.  The  open  brickwork  in  this  stove 
is  divided  into  two  portions  by  a  central  partition  wall  so  as 
to  cause  the  blast  to  pass  up  one  side  and  down  the  other. 
The  principle  is  very  simple  :  the  hotter  air  from  the  heat- 
ing stove  during  the  first  part  of  the  interval  gives  up  heat 
to  the  brickwork  of  the  equaliser,  and  is  thus  reduced  in 
temperature,  and  during  the  last  part  the  cooler  air  absorbs 
heat  from  the  equaliser,  and  is  raised  in  temperature.  In 
this  way  the  general  temperature  of  the  blast  is  kept  nearly 
uniform.  One  equaliser  is  required  for  two  stoves. 

Tapping  the  Furnace. — The  molten  iron  and  slag  collect 
in  the  hearth,  and  as  they  do  not  mix  together  the  heavier 

H 


98  IRON  AND   STEEL. 

metal  sinks  to  the  bottom,  and  the  lighter  slag  rises  to  the 
top.  The  slag  when  it  reaches  the  cinder  notch  runs  from 
the  furnace,  is  collected  in  iron  tubs  or  ladles  mounted  on 
wheels,  and  is  taken  to  the  slag  tip.  The  tubs  are  run  on 
to  a  siding  below  the  level  of  the  furnace,  and  the  slag  run 
into  them  through  a  gutter  which  slopes  from  the  cinder 
notch  and  projects  over  the  siding.  The  slag  is  either 
allowed  to  solidify  before  it  is  dumped  on  to  the  slag  heap, 
or  it  is  taken  there  at  once,  and  run  from  the  ladles  in  the 
fluid  state.  Slag  machines  are  also  used  which  consist  of 
an  endless  chain  of  rectangular  iron  troughs.  These  are 
brought  one  by  one  under  the  slag  gutter,  and  as  they  fill 
are  carried  forward,  water  cooled,  and  their  contents 
dumped  into  trucks  at  the  other  end  of  the  machine. 
Large  quantities  of  slag  are  used  for  various  purposes,  but 
the  supply  is  very  much  greater  than  the  demand.  It  may 
be  granulated  by  running  it  into  water,  and  then  used  for 
making  cement  and  bricks  ;  or  it  may  be  converted  into 
"  slag  wool  "  by  blowing  a  jet  of  steam  against  it  as  it  runs 
from  the  gutter.  It  may  also  be  used  as  "  ballast  "  for  road 
making.  The  metal  is  run  from  the  tap  hole  at  the  bottom 
of  the  hearth.  This  is  closed  by  a  clay  plug  while  the 
metal  is  collecting  in  the  hearth,  and  is  opened  by  driving 
an  iron  bar  through  the  clay  stopping  into  the  hearth.  As 
the  bar  is  withdrawn  the  metal  follows  it,  and  brings  away 
the  remainder  of  the  stopping,  thus  making  a  clear  passage 
for  itself.  When  the  metal  is  to  be  cast  into  pigs  it 
flows  in  a  continuous  stream  down  a  gutter  into  lateral 
channels  called  "  sows."  The  pig  bed  is  made  up  of 
a  large  number  of  open  sand  moulds  into  wiiich  the 
metal  runs  from  the  sows  and  forms  the  pigs.  When  these 
are  sufficiently  cooled  they  are  broken  away  and  removed. 
The  metal  is  always  cast  in  this  way  for  foundry  and  general 
purposes ;  but  for  steel  making,  when  the  blast  furnaces 
are  in  the  neighbourhood  of  the  steel  works,  it  is  now  the 


PIG  IRON  AND   ITS  MANUFACTURE.  99 

common  practice  to  run  the  metal  into  a  tilting  ladle,  and 
convey  it  to  a  "mixer  "  furnace  from  which  it  is  tapped  as 
required. 

Grey  iron  runs  from  the  furnace  readily  and  quietly, 
but  white  iron  is  more  sluggish  and  gives  off  sparks  as  it 
runs.  When  the  tapping  is  finished  a  lump  of  plastic  clay 
is  rammed  into  the  tap  hole,  and  being  rapidly  baked  by 
the  heat  forms  an  effective  stopping.  The  intervals 
between  successive  taps  vary  with  the  rate  of  working. 

The  general  arrangement  of  the  pig  beds  and  slag- 
machines  is  shown  in  the  frontispiece. 

Furnace  Obstructions  of  various  kinds  occur  from  time  to 
time,  and  these  have  to  be  removed  if  the  furnace  is  to 
work  uniformly.  A  twyer  stopped  by  a  slag  nose,  or  other 
cause,  is  usually  opened  by  a  pricker  rod  inserted  through 
the  elbow ;  but  sometimes  it  is  necessary  to  use  a  cartridge 
for  the  purpose,  or  the  twyer  may  have  to  be  removed  while 
the  furnace  is  in  blast.  It  is  interesting  to  see  the  last 
operation  carried  out  by  skilful  workmen.  Another  method 
now  coming  into  use  is  to  direct  a  jet  of  coal  gas  burning  in 
oxygen  (the  oxyhydrogen  flame)  against  the  obstruction, 
and  melt  it  out.  If  the  obstruction  is  metallic,  it  is  only 
necessary  to  heat  it  up  with  the  flame,  and  then  direct  the 
jet  of  oxygen  under  great  pressure  against  it.  The  metal 
in  front  burns,  and  the  heat  developed  melts  that  behind  it, 
and  a  passage  is  blown  through.  The  gases  for  the  blow- 
pipe are  contained  in  steel  cylinders  under  great  pressure. 
The  furnace  man  can  usually  tell  how  a  particular  twyer  is 
working  from  its  appearance  through  the  "  eye."  He  knows, 
for  example,  that  a  bright  twyer  is  doing  more  work  than  a 
glowing  one. 

Other  obstructions  occur  that  may  be  more  difficult  to 
remove.  Thus  the  materials  of  the  charge  when  they  get 
into  the  softening  zone  may  stick  to  the  sides  of  the  boshes 
and  form  a  kind  of  shelf  on  which  the  descending  charge 

H  2 


100  IRON  AND   STEEL. 

lodges.  This  is  termed  a  scaffold,  and  when  the  charge 
recedes  from  underneath  leaving  an  empty  space,  it  may 
give  way,  and  thus  cause  a  slip.  The  furnace  then  resumes 
its  ordinary  working.  Scaffolds  rarely  occur  above  the 
boshes,  and  are  commoner  in  hot  blast  than  in  cold  blast 
working.  They  usually  occur  over  the  twyers,  and  where 
two  are  formed  on  opposite  sides  they  may  gradually  extend 
inwards,  and  form  a  bridge  right  across  the  furnace.  This 
is  the  most  difficult  form  of  scaffold  to  deal  with.  Some- 
times they  extend  right  round  the  furnace  in  the  form  of  a 
ring.  These  obstructions  are  indicated  by  the  irregular 
working  of  the  furnace,  which  influences  the  nature  of  the 
metal,  slag,  and  furnace  gas. 

They  are  located  by  the  appearance  of  the  twyers,  and  by 
sounding  the  level  of  the  charge  in  the  top  of  the  furnace. 
This  is  done  by  inserting  a  long  iron  rod  until  it  touches 
the  charge,  which  is  always  higher  over  the  obstruction. 
Irregular  charging  with  bad  distribution,  soft  or  small  ore, 
weak  coke,  unsuitable  flux,  and  the  internal  shape  of  the 
furnace  are  the  common  causes  of  their  formation.  Various 
means  are  employed  to  dislodge  a  scaffold  after  it  has 
formed.  A  crowbar  may  be  sufficient  when  it  is  just 
above  the  twyer.  The  temperature  of  the  blast  may  be 
increased,  and  petroleum  injected  to  get  a  very  high  tem- 
perature, and  so  melt  it  away.  Special  twyers  are  some- 
times inserted  above  the  ordinary  twyer  level,  and  in  some 
furnaces  means  are  provided  for  doing  this,  otherwise  the 
furnace  has  to  be  cut  through  from  outside.  Suddenly 
cutting  off  and  turning  on  the  blast  will  sometimes  "  jerk  " 
the  obstruction  down. 

American  Blast  Furnace  Practice. — Great  reductions  in  the 
cost  of  blast  furnace  working  have  been  effected  in  the 
United  States  by  the  introduction  of  mechanical  appliances 
for  handling  the  raw  materials  right  from  the  time  they  are 
run  on  to  the  works'  siding  until  they  are  dumped  into  the 


PIG  IRON  AND   ITS   MANUFACTURE. 


101 


top  of  the  furnace.  The  same  may  be  said  of  the  molten 
metal  and  slag  run  from  the  bottom.  The  increase  in  the 
rate  of  production  by  the  use  of  hotter  blast  and  more 
powerful  blowing  engines  has  also  tended  to  reduce  the 
cost ;  while  the  extra  wear  upon  the  furnace  by  this  very 
rapid  driving  has  been  met  by  the  introduction  of  water- 
cooled  plates  into  the  walls 
of  the  boshes  and  the  com- 
bustion zone.  There  has 
been,  generally  speaking, 
no  increase  in  the  size  of 
the  furnaces.  Howe  states 
that  a  single  furnace  in 
Ohio  has  made  no  less  than 
806  tons  of  Bessemer  pig- 
iron  in  twenty-four  hours. 
An  idea  of  the  magnitude  of 
the  operations  entailed  by 
this  rate  of  working  is 
obtained  from  the  state- 
ment that,  roughly,  1,400 
tons  of  ore,  700  tons  of  coke, 
and  400  tons  of  limestone 
have  to  pass  through  the 
furnace  to  produce  the  out- 
put ;  and  that  no  less  than 
4,000  tons  of  air  must  be 

blown  in  at  the  bottom  of  the  furnace,  while  1,200  tons 
of  slag  will  leave  it  with  the  outcoming  metal.  It  is 
questionable  whether  the  primitive  language  of  the  ancient 
ironworker  with  his  goatskin  bellows  would  have  been  of 
much  use  in  helping  him  to  express  his  surprise  at  such 
operations. 

Operations  of  this  magnitude  could  not  be  carried  on 
without  considerable  help  from  mechanical  appliances,  and 


FIG.  18. 


102  IRON  AND   STEEL. 

a  short  description  of  how  it  is  done  will  make  the  matter 
clear.  The  ore,  fuel,  and  flux  are  run  direct  from  hins  into 
the  charging  buckets,  which  are  then  raised  by  a  cable 
hoist  to  the  top  of  the  furnace.  The  loaded  bucket 
A,  Fig.  18,  which  is  fitted  with  a  flange  and  movable 
conical  bottom,  is  then  lowered  on  to  the  top  of  a 
flanged  hopper  B,  that  encloses  the  cup  and  cone-charging 
arrangement,  and  the  conical  bottom  of  the  bucket  is 
allowed  to  drop  a  little,  when  the  charge  falls  out  into 
the  charging  hopper.  The  bucket  is  then  lifted  and  passes 
back  to  receive  another  charge.  When  enough  has 
accumulated  in  the  cup  the  cone  is  lowered,  and  the  charge 
passes  into  the  furnace.  This  is  the  common  method  of 
mechanical  charging. 

The  metal  is  not  tapped  into  the  pig  moulds  direct,  but 
into  a  mounted  ladle,  which  is  then  run  to  the  pig  casting 
machine  (Uehling's),  that  consists  of  a  large  number  of  iron 
pig  moulds  formed  into  an  endless  chain  mounted  on 
sheaves,  on  which  it  moves  round  two  horizontal  drums. 
The  metal  is  run  from  the  tilting  ladle  through  a  funnel 
into  the  moulds  as  they  slowly  pass  under  it.  The  filled 
moulds  are  carried  forwards  and  downwards  into  a  water 
cooling  tank,  in  which  they  are  submerged  during  part  of 
their  journey,  and  the  cooled  pigs  are  dropped  into  a  rail- 
way truck  as  the  moulds  pass  over  the  end  cylinder.  The 
moulds  pass  back  under  the  tank  to  receive  a  fresh  cast. 

Or,  the  metal,  after  it  has  been  tapped  from  the  furnace 
into  the  ladles,  is  passed  on  direct  to  the  Bessemer  shop  for 
conversion  into  steel.  The  slag  is  removed  by  a  machine 
of  similar  construction  to  the  above,  delivered  into  trucks, 
which  hurry  it  off  to  the  slag  tip. 

As  many  as  three,  and  sometimes  four,  hot  blast  stoves 
with  a  total  capacity  about  three  times  that  of  the  furnace 
they  serve  are  used  for  each  furnace.  Only  one  stove  is  "  on 
blast,"  the  others  being  "  on  gas  "  in  the  proper  order. 


PIG  IKON  AND  ITS  MANUFACTURE.  !();] 

The  most  modern  stoves  differ  very  little  in  principle  from 
the  Cowper  stove  described  on  p.  81. 

The  world's  output  of  pig  iron  has  increased  enormously, 
in  fact,  more  than  doubled,  within  the  last  five-and-twenty 
years,  and  from  what  has  been  said  it  is  not  surprising 
that  America  has  shot  far  ahead  of  all  other  iron  producing 
nations  in  this  respect. 

Iron  Alloys. — Pig  metal  containing  a  much  higher  per- 
centage of  other  elements  than  is  usually  present  in  the 
ordinary  pig  is  sometimes  produced  in  the  blast  furnace. 
These  are  the  iron  alloys  or  ferro  alloys  now  so  largely 
used  for  a  variety  of  purposes. 

Ferro  Silicon. — Alloys  containing  up  to  20  per  cent,  of 
silicon  can  be  prepared  with  little  difficulty  in  the  blast 
furnace.  For  this  purpose  it  is  necessary  that  the  charge 
should  be  very  siliceous,  and  the  furnace  worked  at  as  high 
a  temperature  as  possible.  This  means  a  very  hot  blast,  a 
large  fuel  consumption,  and  a  slag  acid  in  character,  so 
that  the  proportion  of  limestone  in  the  furnace  charge 
must  be  reduced. 

Ferro-Manganese. — These  alloys,  which  contain  from  5  to 
85  per  cent,  of  manganese,  are  a  common  product  of  the 
blast  furnace.  When  they  contain  from  5  to  25  per  cent,  of 
manganese  they  are  classed  as  spiegeleisen,  and  when  from  25 
to  85  per  cent,  as  ferro-manganese.  The  general  conditions 
for  their  production  are  very  hot  working  and  sufficient  lime 
to  prevent  too  much  of  the  manganese  from  passing  into  the 
slag.  But  it  cannot  be  kept  out  entirely,  on  account  of  the 
great  fluxing  action  of  its  oxide  MnO.  The  charges  are 
usually  prepared  to  allow  £  to  -J-  of  the  manganese  present 
to  pass  into  the  slag,  according  to  the  richness  of  the  ore 
charge.  The  carbon  is  higher  and  the  silicon  lower  than 
in  ordinary  pig  iron.  The  following  is  a  typical  ferro- 
manganese  :  Mn  =  82-23,  Fe  =  ll'O  ;  C  =  5'95  ;  Si  =  0'2. 

Ferro- Chromium. — This  alloy  is  much  more  difficult  to 


104  IEON  AND   STEEL. 

prepare  in  the  blast  furnace  than  either  of  the  above  alloys. 
The  ore  used  is  the  well-known  chrome  iron  ore,  and  it  is 
usually  smelted  in  a  small  cupola  furnace.  Unless  the  whole 
of  the  chromium  is  reduced  the  slag  becomes  very  pasty, 
due  to  the  presence  of  oxide  of  chromium  in  it.  This 
seriously  interferes  with  the  working  of  the  furnace,  and 
sometimes  stops  it  altogether,  portions  of  the  furnace 
having  to  be  pulled  down  to  remove  the  obstruction.  A 
very  high  temperature  must  be  maintained  by  a  very  hot 
blast,  and  the  fuel  consumption  is  about  three  times  as  great 
as  for  ordinary  pig.  Carbon  is  greedily  taken  up  by  the  alloy, 
and  as  much  as  12  per  cent,  may  be  present.  Forty  per 
cent,  chromium  is  the  highest  for  the  blast  furnace  method. 
Eicher  alloys  were  formerly  made  in  crucibles.  Now  they 
all  come  from  the  electric  furnace.  Fluor  spar,  alkaline  car- 
bonates and  borax  are  often  used  as  fluxes. 

Typical  analysis:  Or  =  65 ;  Fe  =  22 ;  C  =  12 ; 
Si  -  0-4 ;  Mn  =  0'4. 

PIG  IRON. 

The  metallic  product  varies  with  the  general  working  of 
the  furnace,  and  with  the  composition  of  the  charge, 
but  it  is  stated  that  with  care  upwards  of  70  per  cent, 
of  the  particular  grade  worked  for  can  be  obtained. 
The  different  varieties  of  pig  iron  depend  upon  the 
nature  and  proportions  of  the  other  elements  present 
with  the  iron.  The  proportion  of  carbon  generally  lies 
between  2  and  4  per  cent.,  and  when  it  is  practically  all  in 
the  free  or  graphitic  form  the  pig  is  decidedly  grey,  and  its 
fractured  surface  has  a  characteristic  crystalline  appearance 
due  to  the  graphitic  scales  present  in  it.  Grey  pig  is 
usually  siliceous,  and  may  contain  from  0'5  per  cent,  to 
4  per  cent,  of  silicon.  Phosphorus,  sulphur,  and  manganese 
are  present  in  varying  proportions.  Still,  if  non-phosphoric 
ores  are  smelted,  and  the  furnace  is  worked  at  a  high 


PIG  IRON   AND  ITS  MANUFACTURE. 


105 


temperature  with  a  sufficiently  basic  slag,  the  pig  may  he 
remarkably  free  from  both  phosphorus  and  sulphur.  Thus 
very  high  grade  grey  pig  can  be  made  even  with  the  hot 
blast. 

The  different  grades  of  grey  pig  iron  are  indicated  by 
numbers.     Thus,   Nos.  1,   2,   8  and  4  are  foundry  irons. 


No.  4. 


No.  1. 


FIG.  19. 


No.  1  is  the  greyest,  and  has  the  most  open  fracture,  while 
No.  4  has  a  much  closer  grain,  and  is  a  stronger  iron.  No.  4 
forge  is  also  a  grey  iron,  but  is  more  phosphoric  than  the 
corresponding  foundry  iron,  and  is  generally  used  for 
conversion  into  wrought  bars. 

Now,  iron,  carbon,  and  silicon  may  be  regarded  as  the 
normal  constituents  of  grey  pig,  and  it  may  be  taken  as  a 
general  rule,  that  as  the  number  increases  the  proportion 
of  the  carbon  in  the  combined  state  also  increases,  while 
the  percentage  of  silicon  decreases,  and  the  grain  becomes 


106 


IEON  AND  STEEL. 


closer.  But  this  is  merely  a  generalisation,  for  appearances 
are  often  deceitful,  and  experts  are  sometimes  misled  by 
the  fracture  of  the  pig,  which  does  not  depend  entirely  upon 
composition.  Thus  an  iron  may  be  classified  as  No.  1 
that  is  really  No.  2  or  even  No.  3.  For  foundry  purposes 
analysis  is  the  only  true  guide.  The  difference  in  the 
appearance  of  the  fractured  surfaces  of  No.  1  and  No.  4 
grey  pig  is  shown  in  Fig.  19.  The  white  specks  in  No.  1 
are  plates  of  graphite.  When  the  greater  part  of  the 
carbon  is  in  the  combined  form  the  fractured  surface 
of  the  pig  is  white,  crystalline,  and  free  from  graphitic 
scales.  It  is  then  described  as  white  iron.  The  total 
carbon  is  usually  less  than  in  grey  iron,  and  the  silicon 
under  1  per  cent.  As  the  proportion  of  graphite  increases 
patches  of  grey  iron  appear  on  the  white  surface ;  this 
variety  of  pig  is  known  as  mottled  iron.  The  variation  in 
the  form  of  the  carbon  in  the  three  varieties  may  be  shown 
in  a  general  way  as  follows  : — 


Grey. 

Mottled. 

White. 

Graphite          ..... 

3-40 

2-20 

0-12 

Combined  carbon    .... 

0-08 

1-43 

3-17 

Total  carbon    

3-48 

3'4o 

3-29 

In  Staffordshire  the  grade  numbers  are  from  1  to  8,  and 
in  America  from  1  to  10.  The  last  number  in  each  case  is 
white  iron.  In  the  north  of  England  and  Scotland  the 
grades  are  usually  1,  2,  3,  4,  4  forge,  mottled  and  white. 

A  common  form  known  as  "cinder"  pig  is  produced  in 
districts  where  the  puddling  process  is  carried  on.  The 
cinder  from  this  process,  which  is  rich  in  iron,  also  in 
phosphorus  and  sulphur,  is  used  freely  in  the  furnace 
charge,  and  an  impure  pig  results  that  is  distinguished 


PIG  IRON  AND  ITS  MANUFACTURE.  107 

from  the  "  all  mine  "  pig,  which  is  made  entirely  from  ores. 
At  the  present  time  cinder  is  being  used  in  the  furnace 
charge  for  the  production  of  "  basic  "  pig  required  for  the 
Bessemer  and  open  hearth  processes. 

Cold  Blast  Irons. — For  some  purposes  it  is  still  found 
necessary  to  smelt  iron  ores  with  cold  blast,  although  for 
reasons  already  stated  the  cost  of  production  is  considerably 
increased,  and  the  irons  command  a  higher  price.  The 
principal  uses  to  which  these  irons  are  put  are  to  improve 
the  mixture  for  foundry  purposes,  to  make  the  best  qualities 
of  wrought  bar,  and  for  casting  chilled  rolls. 

The  best  Yorkshire  cold  blast  iron  is  smelted  from  a 
calcined  clay  ironstone  with  a  good  quality  coke  low7  in 
sulphur.  The  furnace  charge  consists  of  2^  tons  of 
calcined  ore,  1J  tons  of  coke,  and  1  ton  of  limestone.  The 
output  is  about  25  tons  of  pig  per  day ;  but  this  varies  with 
the  size  of  the  furnace.  With  a  large  furnace  such  as  that 
used  at  Low  Moor  the  output  is  about  350  tons  per  week. 

The  World's  Output  of  pig  iron  for  fifty  years,  and  the 
share  taken  in  it  by  Great  Britain,  is  shown  in  the  following 
table  :— 

Y     ,  Total  output  Great  Britain's  output 

in  millions  of  tons.  in  millions  of  tons. 

1855  ...          6'4         ...         3-2 

1865  ...         9-7         ...         4-8 

1875  .         .         .       14-0         .         .         .         6-,'J 

1885  .         .         .       22-0         ...         7-4 

1895  .         .         .       -*m)         .  7-7 

1905  .          .         .        5-'J'()         .         .         .         9-5 

It  is  not  to  be  expected  that  this  country  could  possibly 
keep  pace  with  America,  considering  the  enormous  resources 
of  that  country,  and  the  great  demand  made  upon  them  by 
its  rapid  development  during  the  last  twenty-five  years. 
When,  therefore,  America  took  the  lead  in  1895,  those 
acquainted  with  the  general  conditions  of  the  industry  were 


108  IRON  AND   STEEL. 

not  at  all  surprised.  Much  the  same  may  be  said  of  the 
position  when  Germany  advanced  to  second  place  in  1903. 
But  the  enormous  increase  in  the  output  is  not  entirely  due 
to  the  activity  of  the  Americans  and  Germans,  for  France 
and  Belgium  have  considerably  increased  their  production 
of  pig  iron  in  the  last  few  years.  The  one  consolation  to 
the  British  ironworker  is  that  his  lower  position  in  the 
iron-producing  world  is  not  due  to  either  want  of  skill  or 
energy  on  his  part,  and  he  must  take  pride  in  the  fact  that 
most  of  the  great  advances  had  their  origin  in  his  own 
country,  or  were  fathered  by  his  own  kin  in  America. 

FOUNDRY  IRONS  AND  THEIR  USE. 

Sulphur  is  one  of  the  most  injurious  impurities  in  any 
form  of  commercial  iron,  and,  perhaps,  the  most  difficult  to 
remove.     It  is  one  of  the  very  few  elements  associated  w7ith 
iron  for  which  no  one  has  a  good  word.     The  iron  smelter 
has,  therefore,  to  take  every  means  of  reducing  the  quantity 
present  in  the  pig  metal,  where  it  is  required  for  foundry 
work  especially,  as  the  simple  melting  process  in  the  cupola 
does  not  remove  it.     The  furnace  conditions  for  smelting 
pig  iron  with  a  low  content  of  sulphur  are  hot  working  and 
a  basic  slag,  and  given  these  conditions,  together  with  raw 
materials  not  too  high  in  sulphur,  good  foundry  irons  are 
produced.     But   hot   working   means   always   a    powerful 
reducing  zone  in  which  silicon  is  reduced  by  carbon  and 
passes  into  the  metal.     The  same  conditions  are  favourable 
for  the  reduction  of  phosphorus  and  the  passage  of  this 
element,  together  with  carbon,  into  the  metal.     So  that  if 
phosphorus  is  barred,  the  ores  used  must  be  non -phosphoric. 
But  phosphorus  has  not  the  bad  reputation  among  foundry- 
men  that  sulphur  has;  in  fact,  it  is  of  more  or  less  advantage 
on  account  of  the  extra  fluidity  it  imparts  to  the  molten 
metal. 


PIG   IRON  AND   ITS   MANUFACTURE. 


109 


Foundry  irons  are  mostly  of  the  grey  variety  on  account 
of  their  high  silicon  content,  and  their  quality  is  presumably 
judged  by  the  appearance  of  the  fracture.  But  the  modern 
foundryman  doubts  his  own  ability  to  give  a  reliable 
judgment  by  fracture  alone.  There  are  not  many  "  tricks 
of  the  trade  "  among  iron  men,  and  an  appearance  such  as 
the  fractured  surface  of  a  pig  which  does  not  depend  entirely 
on  composition,  but  is  influenced  by  rate  of  cooling  and 
other  conditions,  might  deceive  the  seller  as  well  as  the 
buyer. 

The  following  analyses  show  the  variations  in  composi- 
tion of  samples  of  No.  1  and  No.  3  grey  pig  from  different 
sources.  The  other  numbers  vary  in  much  the  same  way  :— 

Typical  Analyses  of  No.  1  Foundry  Irons. 


Combined 

carbon. 

Graphite. 

Silicon. 

Manga- 
nese. 

Phos- 
phorus. 

Sulphur. 

(1)  0-25 
(2)  0-07 
(3)  0-14 

3-oO 
3-49 
3-50 

3-50 
3-15 

2-80 

1-75 
0-25 
1-45 

0-90 
0-68 

0-88 

0-04 

o-oi 

O'Oo 

Typical  Analyses  of  No.  3  Foundry  Irons. 


Staffordshire. 

Derbyshire. 

Northants. 

Combined  carbon 

0-07 

0-40 

0-60 

0-30 

0-40 

O-lo 

Graphite    . 

3-60 

2-70 

2-50 

3-20 

3-20 

3-00 

Silicon,  Si 

2-60 

2-90 

3-30 

2-70 

3-40 

3-00 

Manganese,  Mn 

0-40 

2-30 

0-25 

0-90 

0-40 

0-20 

Phosphorus,  P 

0-90 

1-00 

0-60 

1-40 

1-20 

1-30 

Sulphur,  S 

0-05 

0-04 

0-08 

0-04 

0-04 

0-02 

The    variation    in    the   percentage   of   silicon    is    quite 


110 


IRON  AND  STEEL. 


marked.  But  when  the  furnaces  of  a  particular  maker  are 
working  regularly,  the  numbers  show  a  gradually  decreasing 
content  of  silicon,  and  the  influence  of  this  element  on  the 
structure  of  the  pig  and  the  appearance  of  its  fracture  is 
clearly  brought  out.  The  following  are  analyses  of  the 
first  four  numbers  of  a  well  known  brand  : — 


Carbon. 

Silicon. 

Manganese. 

Phosphorus. 

Sulphur. 

No.  1 

3-M  8 

3-25 

0-782 

0-40 

0-045 

2 

3-38 

2-75 

0-782 

0-40 

0-050 

"     3 

3-38 

2-35 

0-758 

0--JO 

0-058 

„    4        . 

3-38 

2-00 

0-758 

0-39 

0-073 

The  marked  difference  in  the  fracture  of  No.  1  and  No.  4 
is  shown  in  Fig.  19. 

Foundry  Practice. — It  is  very  seldom  that  a  single 
number,  or  a  single  brand  even,  is  used  for  casting  purposes. 
The  general  practice  is  to  make  a  "mixture"  of  different 
numbers  and  different  brands  in  order  to  produce  a  casting 
of  given  composition  ;  and  it  is  clear  that  if  the  composition 
is  judged  from  the  appearance  of  the  fracture  of  the  pigs, 
the  mixing  is  by  pure  rule  of  thumb,  and  the  result  may  or 
may  not  be  that  desired.  The  actual  analyses  of  the  pig 
irons  to  be  used  are  evidently  the  only  sure  guides.  Small 
users  may  have  to  rely  upon  the  maker's  analyses,  but  in 
large  foundries  the  consignments  of  pig  are  all  sampled, 
and  check  analyses  made. 

In  making  the  mixture  the  first  thing  to  consider  is  the 
limit  to  the  content  of  phosphorus.  This  may  vary  from 
0*06  to  2  per  cent.,  the  latter,  however,  only  being  allowable 
for  light  ornamental  castings  in  which  strength  is  of  no 
importance.  The  usual  run  is  under  1  per  cent,  for  general 
engineering  work.  The  content  of  manganese  is  also 


Of    THE 

I    UNIVERSITY    J 


PIG  IRON  AND  ITS  MANUFACTURE.  Ill 

important  on  account  of  its  influence  on  the  structure  and 
properties  of  the  casting.  It  strengthens  the  metal  by 
neutralising  the  effects  of  the  sulphur,  with  which  it  forms 
a  less  dangerous  sulphide  of  manganese,  and  may  even 
cause  some  of  the  sulphur  to  be  eliminated  in  the  melting 
when  high  sulphur  in  the  mixture  is  unavoidable.  It  also 
closes  the  grain  of  the  metal  arid  increases  its  strength 
in  that  way.  The  manganese  varies  up  to  1*5  per 
cent,  in  ordinary  mixtures.  The  influence  of  silicon 
appears  to  be  exerted  mostly  in  decomposing  iron  carbide 
and  setting  free  its  carbon  in  the  form  of  graphite,  so  that 
its  action  is  a  softening  one.  Thus  the  higher  the  silicon, 
the  lower  the  combined  carbon,  and  the  softer  and  weaker 
the  metal  is.  Manganese  acts  in  opposition  to  silicon,  in 
that  it  forms  a  double  carbide  of  iron  and  manganese  which 
appears  to  be  more  difficult  to  reduce.  The  content  of 
manganese  can  be  easily  raised  when  necessary  by  the 
addition  of  ferro-manganese  to  the  ladle  before  casting. 

It  would  be  a  difficult  matter  to  arrange  a  mixture  in 
which  all  the  constituents  were  present  in  the  right 
proportion,  so  that  one  at  least  must  be  treated  somewhat 
loosely,  and  that  one  is  usually  carbon.  The  principal 
thing  is  to  arrange  for  the  proper  content  of  combined 
carbon,  as  it  is  this  that  imparts  the  required  strength  and 
hardness  to  the  cast  metal.  Thus  castings  to  be  turned, 
planed,  etc.,  contain  about  0'2  per  cent. ;  while  those 
required  to  have  considerable  tensile  strength  contain  about 
0*5  per  cent,  of  combined  carbon.  Transverse  strength  is 
imparted  by  0'7  per  cent.,  and  crushing  strength  by  1  per 
cent,  of  the  combined  form.  This  must  be  arranged  for  by 
altering  the  content  of  silicon,  taking  as  the  general  rule 
that  the  lower  the  silicon  is  the  higher  will  be  the  combined 
carbon.  The  amount  of  total  carbon  is  not  of  great 
moment,  but  when  too  much  is  present  it  may  be  reduced 
by  the  addition  of  steel  scrap  of  known  composition.  The 


112  IRON  AND   STEEL. 

content  of  silicon  is  often  varied  by  the  use  of  "  softeners  "- 
that  is,  high  silicon  pig  iron  and  ferro-silicon.     The  extra 
silicon    acts    by   separating   carbon  as  graphite,  and  thus 
softening  the  metal.     These  softeners  are  very  useful  when 
hard  scrap  is  being  worked  up. 

The  general  effect  of  melting  the  mixture  is  to  reduce  the 
content  of  silicon  by  from  0'2  to  0*3  per  cent.  Manganese 
is  oxidised  and  passes  into  the  slag,  and  the  loss  depends 
upon  the  original  content,  but  may  amount  to  0'3  per  cent, 
on  1  per  cent,  and  upwards.  Phosphorus  is  very  little 
affected,  and  sulphur  is  more  likely  to  be  increased  than 
diminished,  by  absorbing  some  from  the  coke  fuel  used  in 
the  melting. 

It  is  seen  that  little  difficulty  should  be  experienced  in 
obtaining  a  mixture  which  in  melting  should  give  a  very 
close  approximation  to  the  required  composition.  No  one 
should  depreciate  the  "  instinct  "  born  of  long  practice,  and 
often  unerring,  that  decides  the  melter  to  throw  in  half  a 
pig  of  this  or  that  brand  to  a  given  mixture  ;  but  at  the 
same  time  it  only  requires  a  little  knowledge  of  percentage 
and  proportion,  together  with  the  analyses  of  the  pigs,  to 
be  reasonably  certain  of  the  result.  In  good  practice,  then, 
the  foundry  manager  has  a  stock  of  different  brands  of  both 
hot  and  cold  blast  irons,  together  with  good  scrap,  ferro- 
silicon,  and  ferro-manganese.  With  these  any  kind  of 
castings  can  be  produced. 

Malleable  Castings. — This  name  is  given  to  a  class  of  small 
castings  made  from  white  and  mottled  pig  irons.  These 
irons  do  not  contain  sufficient  silicon  to  cause  the  carbon  to 
separate  as  graphite  to  any  extent  when  they  are  rapidly 
cooled  from  the  molten  state.  The  mottled  irons  are  used 
for  small  castings  and  the  white  iron  for  larger  ones. 
They  are  very  hard  and  brittle,  and  require  further 
treatment  before  they  are  fit  for  use.  This  will  be  described 
in  Chapter  XII.  The  content  of  silicon  in  the  metal  varies 


PIG  IRON"  AND  ITS  MANUFACTURE.  m 

from  0'4  fco  1  per  cent.,  and  should  not  exceed  this  very 
much,  or  graphite  will  separate  even  in  the  rapidly-cooled 
castings. 

The  Cupola  used  for  melting  pig  iron  in  the  foundry  is  a 
small  ironclad  blast  furnace.  The  blast  is  driven  into  the 
furnace  through  one  or  more  twyers  at  a  pressure  of  J  to 
1  Ib.  per  square  inch,  and  is  supplied  by  either  a  fan  or  a 
Root's  blower.  The  pig  iron  mixture  and  coke,  together 


FIG.  20. — Foundry  Cupola. 

A,  Platform.  D,  Twyers. 

B,  Charging  door.  E,  Drop  bottom, 
c,  Blast  belt. 

with  a  little  limestone  flux,  are  charged  through  the 
charging  door,  and  the  metal  is  practically  fused  on  a  bed 
of  coke  through  which  it  sinks  to  collect  in  the  bottom. 
When  melted  it  is  tapped  into  a  ladle  and  carried  to  the 
moulds.  Sometimes  it  is  tapped  directly  into  the  moulds. 
The  average  consumption  of  coke  may  be  taken  as  1^  cwts. 
per  ton  of  pig  melted.  Most  modern  cupolas  are  supplied 
with  a  "  drop  "  bottom  for  the  ready  removal  of  any  unfused 
material  left  in  at  the  end  of  a  run.  Side  doors  are  also 
used  for  the  same  purpose. 

i.s.  i 


114  IRON  AND   STEEL. 

Moulding. — When  the  selected  mixture  has  been  melted 
in  the  cupola  and  tapped  into  the  ladle  it  is  ready  for 
casting,  and  is  taken  to  the  moulds  prepared  for  its 
reception.  The  preparation  of  these  moulds  is  the  exclusive 
function  of  the  moulder,  and  there  are  few  operations 
requiring  more  skill  than  the  making  of  a  good  mould  from 
a  complicated  pattern.  An  expert  once  said  to  the  writer : 
"  I  can  show  you  how  to  make  a  mould,  but  I  cannot  tell 
you  how  to  do  it." 

The  material  used  is  known  as  casting  sand,  and  contains 
just  sufficient  clayey  matter  to  make  it  bind  when  slightly 
moistened  with  water,  but  not  enough  to  cause  it  to  shrink 
much  when  the  molten  metal  comes  into  contact  with  it. 
The  raw  sand  is  mixed  with  about  10  per  cent,  of  coal  dust, 
and  the  mixture  is  termed  "green  "  sand.  If  dried  before 
use  it  is  known  as  "  dry  "  sand.  The  moulds  are  generally 
made  in  two  parts,  which  are  contained  in  frames  or 
"  flasks  "  to  hold  up  the  sand.  After  the  operation  by 
which  the  pattern  is  properly  worked  into  the  sand  the  two 
halves  are  separated,  the  pattern  removed,  and  the  surface 
of  the  impression  "faced."  The  halves  are  then  put 
together  and  clamped  in  position,  when  the  mould  is  ready 
to  receive  the  metal,  which  is  poured  in  through  a  channel 
or  "  gate  "  leading  from  the  outside  to  the  interior  of  the 
mould.  The  metal  rises  in  the  mould,  and  finally  fills  the 
channel,  when  the  casting  is  finished. 

When  parts  of  the  casting  are  to  be  hollow,  "  cores  "  are 
prepared  of  the  same  shape  as  the  hollows,  and  are  fixed  in 
the  impression  made  by  the  solid  pattern,  so  that  when  the 
mould  is  complete  the  metal  will  run  round  them  and  fill 
every  other  part  of  the  impression.  When  the  casting  is  cold, 
the  cores  are  broken  up  and  removed.  The  pattern  must 
be  prepared  so  that  it  will  leave  the  mould  readily,  and 
undercut  portions  must  be  put  into  the  impression  in  the 
same  way  as  a  core.  Projecting  portions,  called  prints,  are 


PIG  IEON  AND   ITS  MANUFACTURE.  115 

left  on  the  pattern  so  as  to  make  impressions  for  the  ends 
of  the  cores  to  fit  into.  They  are  thus  kept  into  their 
proper  position  in  the  mould. 

No  pattern  is  required  for  "loam"  moulding,  for  the 
mould  is  built  up  of  bricks  or  other  refractory  materials, 
and  faced  with  loam.  The  latter  is  a  very  binding  sand, 
and  is  made  plastic  by  mixing  with  water.  It  is  then 
plastered  over  the  rough  core  and  levelled  to  shape  by 
means  of  templates. 

Some  of  the  moulds  for  machine  and  engine  parts  are 
very  large  and  complicated,  and  require  much  skill  and 
labour  in  the  making.  It  may  be  stated  generally  that 
however  complicated  a  pattern  may  be,  an  expert  moulder 
will  take  an  impression  of  it,  and  reproduce  it  in  cast  iron. 


i  2 


CHAPTER   V. 

THE    REFINING    OF    PIG    IRON    IN    SMALL    CHARGES. 

THE  presence  of  5  per  cent,  or  more  of  impurities  in 
pig  iron  renders  it  quite  unworkable  under  the  hammer, 
although  the  softer  varieties  may  he  either  filed  or 
machined.  Thus  for  iron  which  is  to  he  forged  or  rolled 
the  impurities  must  he  sufficiently  removed  to  render  the 
metal  weldahle  and  malleable.  In  the  early  days  of  cast- 
iron  this  was  done  by  a  refining  process  carried  on  in  a 
small  forge  or  hearth  worked  by  a  blast,  and  by  using 
charcoal  as  fuel. 

The  Swedish  Lancashire  Hearth. — This  refinery  may  be 
taken  as  a  type.  It  consists  of  a  rectangular  closed 
chamber,  the  bottom  and  sides  of  which  are  built  of  cast- 
iron  plates.  The  upper  part  of  the  hearth  communicates 
with  the  stack  by  a  horizontal  flue  through  which  the 
products  of  combustion  pass,  and  in  which  the  pig  iron  is 
placed  to  get  a  preliminary  heating  before  being  drawn  into 
the  hearth  for  manipulation.  The  blast,  heated  to  100°  C., 
is  supplied  through  a  single  inclined  twyer  at  a  pressure  of 
about  one  pound  per  square  inch.  The  metal  used  for  the 
process  is  a  white  pig  iron  low  in  silicon,  phosphorus,  and 
manganese;  and  about  2cwts.  is  drawn  from  the  flue  to  the 
hearth  to  be  melted.  During  the  melting  down  the 
impurities,  principally  carbon,  are  oxidised  by  the  oxygen 
of  the  blast,  and  the  metal  becomes  less  fusible  ;  it  is  then 
broken  up  by  the  workmen,  brought  in  front  of  the  twyer, 


THE   REFINING    OF    PIG   IKON   IN   SMALL   CHARGES.    117 

more  charcoal  added,  and  the  blast  increased.  In  this  way 
the  impurities  are  brought  within  the  limits,  and  the  pasty 
mass  of  refined  iron  is  ready  for  the  mechanical  processes 


FIG.  21. — Swedish  Lancashire  Hearth  (vertical  section). 

A,  Hearth.  E,  Heating  chamber  for  pig. 

V,  Twyer.  1<\  Rod  hole. 

C,  Blast  main.  (7,  Platform. 

D,  Heating  chamber  for  blast.  //,  Chimney. 

of  hammering  and  rolling  into  bars.  The  cinder  obtained 
is  principally  ferrous  silicate,  formed  by  the  oxidation  of 
iron  and  silicon  in  the  refining.  Larger  hearths  with  three 
twyers  were  also  used. 

The  excellent  quality  of  the  iron  produced  by  this  process 


118  IEON  AND   STEEL. 

is  shown  by  the  following  analysis,  which  is  exclusive  of 
iron  :— 

Carbon,  C '05 

Silicon,  Si '01 

Manganese,  Mn    .         .         .         .         .         .  -10 

Phosphorus,  P '02 

Sulphur,  S -01 

In  the  Walloon  process  a  smaller  hearth  is  used,  with  a 
correspondingly  smaller  output,  but  the  metal  is  said  to 
have  more  "  body  "  and  to  be  better  suited  for  use  in  steel 
making. 

The  South  Wales  Process. — It  was  found  that  the  white 
pig  iron  produced  in  furnaces  using  coke  as  fuel  contained 
too  much  sulphur  to  furnish  a  good  refined  iron  ;  so  that 
grey  pig  obtained  by  working  the  furnace  at  a  higher 
temperature,  with  a  more  basic  slag,  and  consequent  reduc- 
tion in  the  sulphur  content,  had  to  be  used.  This  gave 
rise  to  a  modification  of  the  process  by  refining  in  two 
stages.  The  first  stage  is  conducted  in  a  larger  hearth 
with  several  twyers,  and  consists  in  melting  down  the  grey 
pig  to  largely  remove  the  silicon  and  convert  it  into  the 
equivalent  of  white  pig.  The  charge  of  about  5  cwts.  of 
metal  when  perfectly  fluid  is  divided  between  two  smaller 
hearths,  and  the  refining  finished  as  described  above.  By 
having  the  smaller  hearths  at  a  slightly  lower  level  the 
metal  can  be  run  direct  to  them  from  the  larger  hearth  at 
the  conclusion  of  the  melting  down  stage.  But  sometimes 
it  is  tapped  into  a  flat  plate  mould  and  then  broken  up 
while  still  hot  and  tender,  the  broken  pieces  of  "  plate 
metal  "  being  melted  and  finished  as  before. 

This  process  was  used  very  extensively  for  the  production 
of  the  very  malleable  iron  used  in  the  manufacture  of 
"  charcoal  plates  "  for  the  tin  plate  industry.  It  has,  how- 
ever, been  almost  entirely  superseded  by  the  introduction 


THE   REFINING  OF   PIG  IKON  IN  SMALL   CHARGES.     119 

of  ingot  iron ;  but  there  are  still  some  old-fashioned  people 
who  specify  that  the  metal  they  buy  must  be  made  by  this 
process.  There  is  one  forge  still  in  regular  use  within 
twenty  miles  of  Birmingham  in  which  pig  iron  is  refined 
in  a  hearth,  and  the  product  worked  into  sheets  and  bars 
by  water  power.  In  other  districts,  too,  hearths  are  still 
kept  in  readiness  for  the  supply  of  special  orders.  Old 
processes,  like  prejudices,  die  hard. 

The  Puddling  Process. — This  process  is  a  comparatively 
modern  one,  as  it  was  first  used  by  Cort  in  1784.  It 
introduced  quite  a  new  feature  into  the  refining  of  iron,  for 
up  to  that  time  the  metal  to  be  refined  and  the  fuel  used 
to  develop  the  necessary  heat  were  mixed  together  in  the 
same  hearth,  hence  only  a  pure  fuel,  such  as  charcoal, 
could  be  used.  But  in  Cort's  method  the  refining  furnace 
is  divided  into  three  parts  :  (1)  the  grate  in  which  the  fuel 
is  burnt ;  (2)  the  bed  or  hearth  upon  which  the  refining  is 
carried  on  ;  and  (3)  the  chimney  for  creating  the  necessary 
draught.  In  such  a  furnace,  which  belongs  to  the  well-known 
reverbcratory  type,  the  chimney  is  at  one  end  of  the  bed 
and  the  grate  at  the  other ;  so  that  the  flame  and  products 
of  combustion  from  the  grate  must  pass  over  the  bed  to 
reach  the  chimney,  and  by  having  a  low  and  properly 
formed  roof,  materials  placed  on  the  bed  can  be  raised  to 
a  high  temperature  without  coming  into  contact  with  the 
fuel.  Thus  there  is  much  less  risk  of  contamination,  and 
raw  coal  can  be  used  for  firing.  Also,  by  regulating  the 
admission  of  air  an  oxidising  or  reducing  atmosphere  can 
be  maintained  over  the  bed.  According  to  Prof.  Gowland, 
furnaces  based  upon  this  principle  were  used  for  copper 
smelting  as  early  as  1583,  so  that  the  form  of  furnace  was 
well  known  in  Cort's  time. 

Assuming  that  the  cast  iron  to  be  refined  was  similar 
to  that  already  dealt  with  in  the  description  of  the  older 
processes,  carbon  and  silicon  were  the  chief  impurities  to 


120  IEON  AND   STEEL. 

be  removed,  and  Cort's  original  process  is  open  to  a  simple 
explanation.  The  furnace  bottom  was  lined  with  silica 
sand,  and  the  white  iron  heated  upon  it  would  assume  a 
pasty  condition,  not  becoming  perfectly  fluid  at  the  furnace 
temperature.  Then  by  well  exposing  it  to  the  oxidising 
atmosphere  over  the  bed,  oxide  of  iron  would  be  formed, 
and  assist  in  the  oxidation  of  the  silicon  and  carbon.  Thus 
by  keeping  the  pasty  mass  well  stirred  up,  the  metal  would 
gradually  come  to  "nature,"  and  could  then  be  made  up 
into  several  balls  for  removal  from  the  furnace.  The  loss 
of  metal  was  very  large,  for  in  the  production  of  one  ton 
of  bars  two  tons  of  pig  iron  had  to  be  used.  This  would 
mean  the  formation  of  a  considerable  amount  of  cinder, 
which  would  obtain  its  silica  largely  from  the  acid  lining, 
and  the  bed  would  require  frequent  repairs.  Also,  the 
actual  refining  was  very  slow,  from  two  to  three  hours 
being  required  for  the  puddling  of  2J  cwts.  of  pig  iron. 
In  the  palmy  days  of  the  process  it  was  considered  good 
practice  to  obtain  one  ton  of  bars  from  26  cwts.  of  pig. 

The  original  furnace  bottom  was  probably  a  solid  one, 
but  in  1816  Eogers  substituted  an  iron  bottom,  protected 
by  oxidised  iron,  for  the  sand  bottom  ;  this  added  materially 
to  the  life  of  the  bottom,  and  reduced  the  loss  of  metal 
during  refining. 

It  was  found  that  the  white  pig  iron  produced  in  coke 
blast  furnaces  contained  too  much  sulphur  to  furnish  good 
quality  puddled  iron ;  so  that  the  expedient  of  converting 
the  purer,  but  more  silicious,  grey  pig  produced  at  higher 
temperatures  into  white  iron  in  the  coke  refinery  was 
adopted.  This  refinery  was  largely  used  in  Staffordshire. 
Yorkshire,  and  South  Wales  some  fifty  years  ago,  and  is 
still  in  limited  use  in  Yorkshire  for  the  production  of  a 
special  brand  of  iron. 

The  Refinery  or  Running-out  Fire  may  be  described  as 
a  shallow  rectangular  hearth  having  an  area  of  4  square 


THE   REFINING    OF   TIG   IRON   IN   SMALL   CHARGES.     121 

feet  and  a  depth  of  18  inches.  The  back  and  sides  are 
formed  of  hollow  cast  iron  blocks  through  which  water 
can  circulate,  and  the  front  consists  of  a  solid  iron  plate 
containing  the  tap  hole.  A  rectangular  space  above  the 
hearth  is  enclosed  by  two  wrought  iron  side  plates,  two 
swing  doors  at  the  back,  and  a  single  lever  door  in  front, 
the  whole  being  surmounted  by  a  chimney  to  carry  off  the 
products  of  combustion.  The  blast  is  supplied  by  six  twyers, 
three  on  each  side.  They  are  inclined  downwards  at  an 
angle  of  25  to  30  degrees  so  as  to  blow  into  the  hearth, 
and  are  arranged  so  that  they  do  not  blow  against  each 
other. 

To  run  down  a  charge  a  layer  of  coke  is  spread  over  the 
bottom  of  the  hearth  and  blown  up  to  a  red  heat.     The 
blast  is  then  turned  off,  the  doors  at  the  back  opened,  and 
part  of  the  charge  of  grey  pig  iron  thrown  in.     More  coke 
and  pig  iron  are  added,  until  the  full  charge  of  from  one  to 
two  tons  of  metal  is  added  ;  then  the  doors  are  closed,  the 
blast  turned  on,  and  the  charge  melted  down.     During  the 
melting  both    silicon    and  iron    are    oxidised    and  a  fluid 
cinder  formed ;  also  some  carbon  is  oxidised,  together  with 
phosphorus   and    sulphur,    so    that   a   partial    refining   is 
effected.      A  comparison  of  the  analyses  of  the  pig  iron 
used  and  of  the  refined  metal  obtained  shows  that    the 
content  of  sulphur  is  reduced  somewhat,  and  that  of  the 
phosphorus  rather  more.     This  is  due   to  the  very  basic 
character  of  the  cinder  formed  by  the  oxidation  of  iron  and 
silicon.     When  the  metal  has  run  down  it  is  tapped  into  a 
shallow  iron  mould,  which  is  so  supported  that  water  can 
circulate  underneath  to  keep  it  cool.     The  metal  is  thus 
rapidly  cooled  and  the  carbon  kept  in  the  combined  form, 
with  the  result  that  a  white  iron  is  obtained.     The  cinder, 
which  runs  from  the  hearth  with  the  metal,  is  tapped  from 
the  surface  into  another  mould  when  the  metal  itself  has 
solidified.     The  cooling  of  the  metal  is  also  hastened   by 


122  IEON   AND   STEEL. 

throwing  water  on  to  it.     The  "  plate  metal  "  thus  obtained 
is  broken  up  and  puddled. 

In  1830,  J.  Hall,  of  the  Bloomfield  Ironworks,  Stafford- 
shire, discovered  the  effect  of  adding  oxide  of  iron  to  the 
puddling  charge  in  the  furnace,  and  noticed  the  boiling  up 
due  to  the  rapid  oxidation  of  the  carbon  by  the  oxygen  of 
the  rich  oxides  added.  This  no  doubt  suggested  the 
modern  process  of  "  pig  boiling,"  which  is  now  almost 
exclusively  used  in  the  manufacture  of  wrought  iron  by  the 
puddling  process. 

The  Puddling  Process  of  To-day. — The  puddling  furnace, 
a  vertical  section  of  which  is  shown  in  Fig.  22,  is  a  rect- 
angular fire-brick  structure,  about  12  feet  long,  4  feet  wide, 
and  6  feet  high,  cased  outside  with  iron  plates,  which  are 
held  in  close  contact  with  the  brickwork  by  means  of  tie 
rods  that  pass  along  and  across  the  structure,  and  are  kept 
in  position  by  nuts  screwed  on  the  ends.  The  low  roof  is 
slightly  arched  across  the  direction  of  its  length,  and  slopes 
down  a  little  towards  the  flue-bridge.  The  grate  is  at  one 
end,  and  is  separated  from  the  bed  by  the  fire-bridge,  which 
stretches  right  across  the  furnace.  The  grate  bars  are 
supported  on  bearers  let  into  the  opposite  walls.  A  rect- 
angular opening  in  the  working  side  of  the  furnace,  about 
12  inches  above  the  bars,  communicates  with  the  grate 
space,  and  is  used  to  feed  the  grate  with  fuel  during  the 
operation.  There  is  no  door  to  this  opening,  and  it  is 
usually  closed  with  lumps  of  coal  in  the  intervals  of  firing. 
The  foundation  of  the  bed  is  formed  of  iron  plates,  and  is 
supported  either  on  iron  standards,  or  on  brickwork  built 
out  from  the  side  walls.  It  is  so  arranged  that  air  can 
freely  circulate  under  it  to  keep  it  cool.  The  side  plates  are 
solid,  but  the  fire-bridge  and  flue-bridge  are  hollow 
castings  through  which  air  can  freely  pass.  The  fire-bridge 
is  cased  with  fire-brick  on  the  grate  side  and  top,  the 
brickwork  projecting  a  little  over  on  the  bed  side ;  the  flue- 


THE   EEFINING   OF   PIG   IRON  IN   SMALL  CHARGES.    123 

bridge  is  protected  in  a  similar  manner.  The  working 
doorway  opens  on  to  the  middle  of  the  bed,  and  is  furnished 
with  a  door  suspended  by  a  chain  from  the  end  of  a  lever, 
and  is  kept  in  position  by  guides  at  the  sides.  It  is  readily 
raised  or  lowered,  as  it  is  nearly  balanced  by  a  weight  at 
the  other  end  of  the  lever.  The  door  itself  consists  of  an 


FIG.  22. — Puddling  Furnace  (vertical  section). 

A ,  Working  bed.  E,  Chimney. 

/>,  Working  door.  F,  Fire-bridge. 


C,  Firing  door. 

D,  Grate. 


G,  Staff-hole. 
If,  Damper. 


iron  frame  lined  with  fire-bricks,  and  has  a  small  opening 
called  the  stopper  hole,  in  the  middle  of  the  bottom  edge. 
The  heavy  projecting  piece  of  iron  on  which  the  door  rests 
when  it  is  down  is  known  as  the  fore  plate  and  beneath  it 
is  the  cinder  notch,  through  which  the  cinder  is  tapped  from 
the  bed.  The  fore  plate  is  used  as  a  rest  for  the  tools  in 
working  the  furnace. 

The  flue- bridge  slopes  down  somewhat  to  the  opening 
into  the  stack  which,  when  used  for  a  single  furnace,  is 
about  40  feet  high.  A  tall  chimney  is  necessary  to  give  the 
requisite  draught,  but  it  must  be  under  control.  This  is 
effected  by  a  damper  on  the  top,  which  can  be  raised  or 


124  IRON   AND   STEEL. 

lowered  by  means  of  a  chain  suspended  from  the  end  of  a 
lever,  and  within  reach  of  the  puddler.  Sometimes  several 
furnaces  are  connected  to  one  high  stack  ;  in  that  case  the 
flues  from  the  several  furnaces  are  controlled  by  their  own 
dampers.  When  the  waste  heat  of  the  furnace  is  utilised 
to  raise  steam  the  flame  and  products  of  combustion  pass 
through  a  boiler  fixed  over  the  top  of  the  furnace  before 
passing  to  the  flue.  A  portion  of  the  boiler  can  be  seen  in 
Fig.  23. 

In  preparing  the  bed  for  work  the  iron  bottom  and  side 
plates  are  covered  with  a  protecting  layer  of  material  rich 
in  oxides  of  iron.  This  is  effected  by  spreading  a  layer  of 
crushed  tap  cinder  of  good  quality  (best  tap)  over  the 
bottom,  and  then  firing  to  soften  it.  This  is  again  covered 
with  a  layer  of  hammer  scale  and  haematite  ore  about 
2  inches  thick.  Then  the  side  plates  are  "  fettled "  by 
ramming  "  blue  billy  "  (roasted  pyrites)  and  "  bull-dog  " 
(roasted  tap  cinder)  all  round  the  sides  and  ends  under  the 
projecting  brickwork,  and  levelling  up  the  banks  with 
puddler's  ore,  or  calcined  pottery  mine.  This  is  a  black- 
band  ore  found  in  the  pottery  districts  of  Staffordshire. 

The  selection  of  the  various  materials  for  forming  the 
bed  depends  to  some  extent  on  the  kind  of  pig  to  be 
puddled  and  the  quality  of  the  product  expected.  The 
purer  materials  are  used  in  the  production  of  the  better 
qualities  of  wrought  iron.  Also,  with  a  very  siliceous  or 
"hungry "pig  iron  the  fettling  is  made  as  refractory  as 
possible. 

The  Process.— The  coal  used  for  firing  is  of  the  free 
burning,  bituminous  variety,  for  a  caking  coal  would  coke 
to  a  solid  mass  in  the  grate,  and  hinder  the  draught.  It 
should  also  be  fairly  free  from  ash  to  avoid  excessive 
clinkering  of  the  bars.  One-third  lumps  and  two-thirds 
fine  are  used,  and  about  25  cwts.  is  consumed  per  ton  of 
puddled  bars  produced.  The  following  is  a  general  descrip- 


THE  REFINING   OF   PIG  IROX  IN   SMALL   CHARGES.    125 

tion  of  the  process  :  The  furnace  bottom  being  hot  and 
in  good  condition,  about  f  cwt.  of  fluxing  cinder  (hammer 
slag)  is  first  shovelled  through  the  working  door  on  to  the 
bed  ;  then  the  charge  of  about  4J  cwts.  of  pig  iron  is  thrown 
in  and  the  door  closed.  The  pig  iron  commonly  used  for  the 
puddling  process  is  hot  blast  metal  of  either  the  grey  or 
mottled  variety  (forge  pig),  and  contains  all  the  elements 
usually  present  in  pig  iron,  namely,  carbon,  silicon,  man- 
ganese, phosphorus  and  sulphur ;  but  the  last  element 
should  be  low  if  good  quality  iron  is  to  be  produced.  Now 
it  will  be  well  to  consider  how  these  elements  are  eliminated 
from  the  metal  during  the  process.  With  the  exception  of 
the  carbon,  they  are  present  in  the  pig  as  compounds  of 
iron,  and  to  separate  them  from  the  metal  it  is  necessary 
that  they  should  be  converted  into  oxides,  and  that  these 
oxides  should  be  completely  removed  from  the  main  mass 
of  metal.  In  Cort's  process  this  oxidation  was  said  to 
depend  largely  on  the  oxygen  of  the  air,  oxide  of  iron 
being  first  formed  and  then  acting  as  a  carrier  of  oxygen 
to  the  impurities  in  the  main  mass  of  metal.  In  wet 
puddling  the  oxygen  is  supplied  largely  by  the  oxides  in  the 
fettling,  although  the  air  no  doubt  plays  an  important 
part.  It  would  appear  that  silicon  and  carbon  are  easily 
removed,  and  that  manganese  offers  no  difficulty ;  but  the 
last  portions  of  the  phosphorus  are  difficult  to  get  rid  of, 
and  sulphur  is  always  a  troublesome  impurity  to  deal 
with. 

Both  the  red  oxide,  Fe^Oa,  and  the  black  oxide,  Fe304, 
no  doubt  assist  in  the  refining,  but  it  is  usually  con- 
sidered that  the  latter  plays  the  more  important  part.  The 
following  gives  a  general  view  of  the  changes  : — 

Silica,  SiO2  )  combines  f  Ferrous  Oxide        [  To  form 

5   (  Phosphoric  Oxide,  P-2O-,  j      with       |  Manganous  Oxide  j  fluid  cinder. 
T3     Manganous  Oxide,  MnO 

;|  j  Carbon  Monoxide,  CO      j  burns  to  I  Carbon  Dioxide,  CO-> 


Silicon 

Phosphorus 

Manganese 

Carbon 

Sulphur 


Sulphur  Dioxide,  SO2 

only  partially 


126 


IEON  AND  STEEL. 


Oxides  of  Iron 


J  Ferrous  Oxide,  FeO 
§  1  Metallic  Iron 


I 
111 


Partly 

{  oxidised  to  !-  Magnetic  Oxide,  Fe.(O4. 
form 


The  fluid  cinder  is  the  receptacle  for  all  the  impurities 
that   leave  the  refining    metal,    except  the  carbon  which 


FIG.  23. — Working  Side  of  Puddling  Furnace. 

finally  escapes  as  carbon  dioxide,  and  probably  a  small 
portion  of  the  sulphur,  which  escapes  as  sulphur  dioxide. 
The  larger  proportion  of  the  cinder,  often  upwards  of  80  per 
cent.,  consists  of  the  monosilicate  of  iron,  2FeO.Si02,  the 
remainder  being  made  up  of  ferric  oxide,  phosphoric  oxide, 
manganous  oxide,  lime  and  alumina. 

The  question  then  arises  as  to  how  the  refining  is  actually 
effected  in  the  furnace.  The  oxidation  of  iron  itself  by  the 
free  oxygen  in  the  furnace  gases  would  result  in  the  forma- 
tion of  the  black  oxide,  Fe304 ;  and  a  similar  change  would 


THE   REFINING   OF   PIG  IRON   IN   SMALL   CHARGES.    127 

take  place  between  the  various  impurities  and  this  free 
oxygen,  resulting  in  the  formation  of  their  oxides,  should 
they  come  into  contact.  The  impurities,  however,  are 
shielded  more  or  less  by  the  large  mass  of  iron  present. 
But  they  are  all  capable  of  reducing  oxides  of  iron  to  the 
metallic  state,  so  that  it  is  most  probable  that  these  oxides 
are  the  chief  oxidisers,  although  they  may  be  formed  in  part 
by  the  atmospheric  oxidation  of  the  iron  itself.  Now  the 
better  the  contact  between  the  oxidising  material  and  the 
bodies  to  be  oxidised  the  more  readily  does  the  oxidation 
take  place.  The  contact  between  solids  is  very  imperfect, 
and  reaction  between  them  correspondingly  slow  ;  but  the 
contact  between  solid  and  liquid,  or  between  liquid  and 
liquid,  is  much  more  intimate,  and  reaction  between  them 
takes  place  much  more  rapidly.  Ferric  oxide  is  a  some- 
what refractory  body,  but  when  strongly  heated  is  converted 
into  the  more  fusible  black  oxide.  Therefore  the  latter 
would  appear  to  be  the  more  probable  oxidiser.  Ferrous 
oxide  in  the  form  of  ferrous  silicate,  although  quite  fluid  at 
the  furnace  temperature,  is  not  so  readily  reduced  as  the 
higher  oxides,  for  not  only  is  the  ferrous  oxide  more 
difficult  to  reduce,  but  also  its  combination  with  silica 
increases  its  stability.  But  this  fluid  cinder  will  dissolve 
the  black  oxide  and  thus  bring  it  into  close  contact  with  the 
material  to  be  oxidised.  Siemens  advocated  the  black 
oxide  theory  of  refining,  and  Snelus  was  of  opinion  that 
ferric  oxide  plays  the  more  important  part,  but  the  former 
explanation  is  the  one  mostly  accepted.  If,  however,  the 
black  oxide  is  regarded  as  complex  in  constitution,  and  is 
represented  by  the  formula  FeO.Fe203j  then  it  may  be 
looked  upon  as  the  medium  for  carrying  the  otherwise 
infusible  Fe203  into  the  liquid  cinder,  and  thus  increasing 
its  oxidising  power.  Whatever  may  be  the  true  explanation, 
the  refining  is  very  rapid,  and  a  considerable  quantity  of 
metal  must  be  reduced  from  the  cinder.  The  total  iron  in 


128  IEON  AND   STEEL. 

the  finished  product  is  usually  greater  than  the  total  iron 
in  the  pig  itself,  and  this  can  only  be  accounted  for  by  the 
reduction  of  iron  from  the  fettling.  Say  that  the  loss  in 
puddling  is  from  3  per  cent,  to  5  per  cent,  between 
pig  and  bar,  and  that  the  pig  contains  6  per  cent,  of  impuri- 
ties, this  would  show  a  gain  of  from  1  per  cent,  to  3  per 
cent,  of  metal ;  but  when  the  loss  due  to  oxidation  while 
the  balls  are  standing  in  the  furnace,  and  are  being  worked 
into  bars,  is  taken  into  consideration  it  is  seen  that  the 
quantity  of  iron  reduced  from  the  fettling  must  be  con- 
siderable. This  is  by  no  means  an  extreme  case,  for  it  is 
not  unusual  to  obtain  the  same  or  even  a  greater  yield  of 
bar  than  of  pig  charged.  But  there  is  no  reason  why  silica, 
for  instance,  should  not  partially  reduce  the  higher  oxide, 
and  thus  produce  a  base  for  the  silica  formed,  thus  :— 

Si  +  Fe304=:  2FeO.Si02  +  Fe. 
Ferrous  Silicate 

The  equations  usually  given  to  show  the  oxidation  of  the 
various  impurities  are  as  follows  : — 

/i.  Si  +  02  =  Si02 

Silicon          ]  ii.  Si  +  2Fe304  =•  Si02  +  6FeO 
liii.  2Si  +  Fe304  —  2Si02  +  3Fe 

fi.  4P  +  502  =  2P205 

Phosphorus -jii.  2P  +  5Fe304  =  P205  +  15FeO 
liii.  8P  +  5Fe304  =  4P205  +  15Fe 

[i.  2Mn  +  02  =  2MnO 

Manganese  \  ii.  Mn  +  Fe304  =  MnO  +  3FeO 
(iii.  4Mn  +  Fe304  =  4MnO  +  3Fe 

(i.  C  +  Fe304  =  CO  +  3FeO 
Iii.  4C  +  Fe304  =  4CO  +  BFe 

The  removal  of  sulphur  is  somewhat  obscure,  and  some 
authorities  state  that  it  is  not  oxidised  at  all.  It  is  pro- 
bable, however,  that  some  sulphur  dioxide  is  formed  and 


THE  REFINING  OF   PIG  IRON  IN   SMALL  CHARGES.     129 

escapes,  and  that  the  remainder  of  that  eliminated  passes 
into  the  cinder  as  sulphide  of  iron  or  manganese.  The 
presence  of  manganese  in  the  charge  helps  in  the  elimina- 
tion of  both  phosphorus  and  sulphur,  for  the  metal  acts  as 
a  cover  to  the  carbon,  and  thus  prolongs  the  fluid  stage,  so 
that  the  phosphorus  is  more  perfectly  oxidised.  It  also 
readily  combines  with  the  sulphur,  and  carries  it  into  the 
cinder. 

The  part  taken  by  ferrous  oxide  is  twofold :  part  of  it 
unites  with  silica  and  phosphoric  oxide  to  form  silicate  and 
phosphate  of  iron  respectively,  and  part  of  it  is  oxidised  to 
the  black  oxide  again,  which  thus  acts  as  a  carrier  of 
oxygen  to  the  charge.  It  is  sometimes  stated  that  the 
phosphorus  is  largely  removed  as  phosphide  of  iron, 
squeezed  out  during  the  shingling,  but  this  is  hardly  borne 
out  by  the  composition  of  the  hammer  slag. 

It  will  now  be  easy  to  follow  the  changes  taking  place  in 
furnace  as  the  charge  works  down.  In  describing  the 
process  it  is  usual  to  divide  it  into  stages,  although  these 
naturally  run  into  one  another  in  the  actual  working. 
They  are — 

I.  The  Melting  Stage,  in  which  the  pig  metal  put  into  the 
furnace  as  described  above  is  melted  down  into  a  liquid 
bath  on  the  bed  together  with  the  fluxing  cinder  ;  and  the 
most  uniform  results  are  obtained  when  the  two  melt  simul- 
taneously.    In  the  interval  the  puddler  watches  his  charge, 
and  turns  the  pigs  over  to  ensure  uniform  heating,  and 
when  the  melting  is  well  on  the  way  stirs  up  the  fluid 
portion  collecting  on  the  lower  part  of  the  bed.    The  melting 
stage  occupies  about  35  minutes,  in  which  oxidation  goes  on 
freely.     Silicon,  manganese  and  iron  are  rapidly  oxidised, 
and  phosphorus  to  a  smaller    extent.      The  oxides   thus 
formed  pass  into  the   cinder.     Towards  the  end  the  bath 
settles  down,  and  becomes  clear. 

II.  The  Fluid  Stage.— The  temperature  of  the  bath  is 
i.s.  K 


130  IRON   AND    STEEL. 

kept  up  while  the  puddler  thoroughly  mixes  or  "  rabbles  " 
the  charge,  thus  bringing  the  rich  cinder  and  the  metal 
into  intimate  contact.  The  remainder  of  the  silicon  and 
manganese,  and  a  further  portion  of  the  phosphorus,  are 
oxidised  and  pass  into  the  cinder.  This  stage  occupies 
from  7  to  10  minutes,  and  towards  the  end  jets  of  blue 
flame  appear  on  the  surface. 

III.  The  Boiling  Stage. — The  damper  is  lowered  to  reduce 
the  draught  somewhat.     The  surface  of  the  bath  now  pre- 
sents the  appearance  of  boiling,  due  to  the  rapid  escape  of 
carbon  monoxide  formed  by  the  oxidation  of  the  carbon. 
The  jets  of  gas,  "puddlers'  candles,"  burst  through  the  sur- 
face and  burn  with  a  blue  flame,  and  the  bath  rises  several 
inches;   the  cinder  overflows  and  runs  over  the  fore  plate. 
This  portion  of  the  cinder  is  known  as   "  boilings."     The 
mass  is  then  well  rabbled  to  prevent  the  iron  from  sinking 
to  the  bottom.     The  refining  metal  is  now  becoming  pasty, 
due  to  the  rise  in  the  melting  point  of  the  purer  iron. 
Small  patches  of  bright  metallic-looking  matter  appear  in 
different  parts  of  the  bath,  and  grow  larger.     The  iron  is 
now  coming  to  nature.     This  stage  lasts  about  25  minutes. 

IV.  The  Balling  Stage. — The  puddler  has  now  to  gather 
the  bright  patches  of  purified  metal  together,  and  form  them 
into  balls  of  about  80  pounds  each,  turning  them  over  to 
get  them  uniformly  heated.      Oxidation    of    the  metal   is 
prevented  as  much  as  possible  by  keeping  the  damper  down, 
but  at  the  same  time  the  temperature  of  the  furnace  must 
be  maintained  so  that  the  puddled  balls  may  be  hot  enough 
for  the  shingling  operation.     The  cinder  is  tapped  through 
the   cinder  notch  into  small  iron  waggons.     The  balling 
stage   lasts    about    15   minutes,    and  when    the   balls   are 
drawn  from  the  furnace  on  to  the  iron  trolley,  by  which 
they  are  taken  to  the  forge,  the  puddler's  work  is  done. 
The  full  time  of  working  off  a  charge  is  about  1^  hours  ; 
but  this  depends  somewhat  on  the  skill  of  the  workmen,  as 


THE   BEFINING   OF   PIG   IEON  IN  SMALL   CHARGES.     131 


well  as  on  the  character  of  the  pig  iron  to  be  treated.  A 
puddler  and  his  underhand  can  work  through  6  heats  per 
day,  and  if  Longfellow's  lines, 


;'  Something  attempted,  something 
Has  earned  a  night's  repose," 


done, 


are  true  of  the  blacksmith,  still  more  are  they  true  of  the 
puddler,  than  whom  no  man  endures  harder  or  more 
exhausting  labour. 

Materials  and  Products. — Pig  iron  for  puddling  is  usually 
a  close-grained,  strong,  grey  iron,  No.  4  forge,  but  mottled 
iron  is  also  used.  When  a  very  soft,  ductile  iron  is  required 
for  special  purposes,  the  puddling  charge  consists  of 
"  foundry  irons,"  and  the  other  materials  are  carefully 
selected.  A  typical  pig  may  be  said  to  have  the  following 
compositions,  exclusive  of  iron  : — 

Carbon,  C 3'5 

Silicon,  Si 1-5 

Manganese,  Mn TO 

Phosphorus,  P TO 

Sulphur,  S variable. 

The  tap  cinder  is  usually  described  as  "boilings,"  and 
"  tappings,"  the  latter  of  which  is  the  purer,  as  it  is  tapped 
from  the  furnace  towards  the  close  of  the  process.  The 
following  analyses  given  by  Turner  show  the  difference  in 
the  composition  of  the  two  portions  of  tap  cinder  usually 
obtained. 


Boilings. 

Tappings. 

Ferric  Oxide,  Fe2O«    . 
Ferrous  Oxide,  FeO   . 
Silica,  SiO-2          .                            . 
Phosphoric  Oxide,  P.205 
Not  determined  .                             .         . 

6-94 
62-61 
19-45 
6-32 
4-68 

12-90 
64-62 
15-47 
3-90 
3-11 

100-00 

100-00 

K    2 


132  IEON  AND   STEEL. 

Manganous  oxide,  MnO ;  lime,  CaO ;  magnesia,  MgO ; 
alumina,  A1203,  and  sulphur  are  generally  present  in  small 
quantities,  and  are  included  in  the  "  not  determined  "  given 
above. 

Shots  of  metal  are  often  present  in  the  "boilings,"  and 
can  be  separated  from  the  powdered  cinder  by  a  magnet. 
This  might  be  expected,  as  the  cinder  in  swelling  up  is  sure 
to  bring  away  portions  of  the  metal  entangled  in  it. 

Hammer  slag  is  purer  and  richer  in  oxides  of  iron  than 
the  tappings,  for  oxidation  of  the  metal  takes  place  during 
the  shingling,  and  the  oxides  formed  mingle  with  the 
expelled  cinder. 

Bull-dog  is  the  refractory  residue  obtained  by  the 
calcination  of  tap  cinder  in  a  free  current  of  air.  The 
calcination  is  carried  on  in  small  kilns.  Part  of  the  tap 
cinder  liquefies  and  separates  from  the  main  mass,  bringing 
with  it  the  greater  part  of  the  phosphates.  It  either  settles 
on  the  bottom  of  the  kiln,  or  drains  away  through  special 
openings.  It  is  more  siliceous  than  tap  cinder,  and  is 
known  as  "  bull-dog  slag."  The  bull-dog  itself  consists 
largely  of  ferric  oxide  and  free  silica.  The  mode  of  forma- 
tion may  be  expressed  by  the  equation  : 

2  (2FeO.Si02)  +  02  =  2Fe203  +  2Si02. 

It  is  used  to  a  limited  extent  in  the  fettling  of  the  furnace 
bottom. 

Blue  billy  or  purple  ore  is  the  oxide  residue  left  in  the 
pyrites  burners  used  for  roasting  iron  pyrites  in  the  manu- 
facture of  sulphuric  acid.  When  it  is  used  for  fettling  it 
should  be  low  in  sulphur,  less  than  0'5  per  cent.,  and  free 
from  copper,  which  is  often  present  in  small  quantities  in 
pyrites,  for  both  these  elements  tend  to  make  the  finished 
metal  "  red  short."  Spanish  cuperiferous  pyrites  that 
has  been  roasted  for  sulphuric  acid,  and  the  residue 


THE   REFINING   OF   PIG  IRON  IN  SMALL   CHARGES,     13:3 

treated  for  the  extraction  of  its  copper,  furnishes  a  good 
quality  purple  ore  containing  upwards  of  95  per  cent,  of 
ferric  oxide. 

Pottery  mine  is  a  black  band  ore  containing  manganese, 
which  occurs  in  the  pottery  district  of  Staffordshire.  It  is 
calcined  for  use  in  the  puddling  furnace,  and  in  the  calcined 
state  is  rich  in  oxides  of  iron. 

Best  tap  is  the  cinder  from  a  mill  furnace  worked  with  an 
oxide  bottom.  It  contains  about  94  per  cent,  of  iron  oxides, 
and  only  3  per  cent,  of  silica.  When  it  can  be  obtained  it 
takes  the  place  of  ore  in  the  fettling. 

Hammer  scale  consists  principally  of  the  black  oxide, 
Fe304,  and  is  collected  from  round  the  hammers  and  rolls 
used  in  forging  and  rolling  re-heated  iron. 

The  following  materials  are  given  by  Prof.  Turner  as  the 
average  quantities  for  a  "  turn,"  which  usually  consists  of 
6  heats,  in  the  manufacture  of  best  Staffordshire  iron.  It 
gives  a  good  idea  of  the  intake  and  output  of  a  furnace  : 

Pig  iron         .         .  .  .  .25  cwts.  2  qrs. 

Hammer  slag        .  .  .  .       4    ,,     0    ,, 

Best  tap        .         .  .  .  .       3    ,,     0    ,, 

Bull-dog        .         .  .       2    „     2    „ 

,,        (powdered)  .  .  1    ,,     2    ,, 

Purple  ore    .         .  .  .  .       0    ,,     3    ,, 

The  output  would  be  about  25  cwts.  of  puddled  bars,  and 
13  cwt.  of  tap  cinder. 

It  is  not  unusual  when  the  pig  and  fettling  suit  each 
other,  and  the  puddler  is  skilful,  for  the  yield  of  bars  to  be 
heavier  than  the  charge  of  pig  iron  put  into  the  furnace.  In 
the  production  of  common  iron  the  quantity  of  fettling  used 
is  less  than  that  given  above,  and  less  care  is  taken  in  its 
selection.  Also  the  yield  is  usually  less  than  the  pig 
charged,  the  difference  amounting  to  from  3  per  cent,  to 
5  per  cent.  That  is,  a  ton  of  pig  produces  from  19  cwts,  to 


134  IEON  AND   STEEL. 

19J  cwts.  of  bars.  But  as  there  is  often  as  much  as  7  per 
cent,  of  impurity  removed,  some  iron  must  be  reduced  from 
the  fettling,  and  pass  into  the  refined  metal. 

A  pig  high  in  silicon  and  phosphorus  is  said  to  be 
"  hungry,"  and  uses  up  the  fettling  very  fast,  so  that  a 
purer  and  more  refractory  fettling  should  be  employed. 
Generally  much  care  is  taken  in  proportioning  the  quantity 
and  qualify  of  the  fettling,  for  if  the  cinder  is  deficient  too 
much  of  the  iron  itself  will  be  oxidised,  the  cinder  will 
thicken,  and  be  unable  to  do  its  work  properly,  with 
consequent  deterioration  of  the  product. 

Mechanical  Puddling. — For  many  years  the  puddling  pro- 
cess was  responsible  for  the  production  of  such  constructive 
ironwork  as  could  not  be  made  of  cast  iron,  and  much 
attention  was  given  to  such  modifications  of  it  as  would 
reduce  the  excessive  labour  required,  and  increase  the  out- 
put. Apparatus  was  designed  in  connection  with  stationar}7 
furnaces  to  relieve  the  puddler,  and  among  the  most 
successful  were  those  of  Pickles,  Eastwood,  and  Clough. 
In  all  these  an  arrangement  of  levers,  supported  on  a  frame 
above  the  top  of  the  furnace  and  worked  by  a  small  engine, 
gives  a  to  and  fro  motion  to  the  rabble  across  the  bed,  and  a 
similar  motion  at  right  angles  to  this.  These  two  motions 
compound  and  give  to  the  rabble  a  stirring  motion  that  can 
be  directed  to  any  part  of  the  bed  by  the  puddler,  who  holds 
the  free  end  of  the  rabble.  It  is  worked,  as  usual,  through 
the  stopper  hole,  but  the  puddler  is  relieved  of  much  of  the 
labour  of  rabbling.  The  drawback  to  the  use  of  all  these 
mechanical  contrivances  is  that  they  cannot  do  the  balling 
up,  and  this  is  really  the  heaviest  part  of  the  work.  There- 
fore they  never  came  into  very  general  use. 

With  regard  to  the  increased  output,  larger  furnaces  were 
built  with  doors  on  both  sides,  so  that  the  charge  could  be 
worked  simultaneously  by  the  puddlers  and  their  under- 
hands.  A  heavier  charge  could  thus  be  worked,  but  the 


THE   REFINING   OF   PIG   IRON  IN  SMALL   CHARGES.     135 

product  was  not  so  uniform  on  account  of  the  difficulty  of 
keeping  the  temperature  equal,  and  of  providing  men  of 
equal  skill  for  the  two  sides.  Still,  such  furnaces  were 
found  to  be  economical  of  fuel  and  fettling.  A  still  larger 
furnace  with  four  working  doors,  two  on  each  side,  was 
tried  in  America. 

Revolting  Furnaces. — A  measure  of  success  was  obtained 
by  the  use  of  revolving  beds,  some  of  which  were  made  to 
revolve  round  a  horizontal  axis,  and  others  round  an  axis 
slightly  inclined  to  the  vertical.  But  as  such  furnaces  are 
now  practically  out  of  use,  only  a  short  account  of  them 
need  be  given. 

The  Danks  Furnace.  —  This  is  a  r  ever  beratory  furnace,  of 
which  the  middle  portion  or  bed  consists  of  a  cast  iron 
cylinder  with  conical  ends.  The  cylinder  is  four  feet  long 
and  five  feet  three  inches  in  diameter,  and  is  made  of 
segments  bolted  together.  It  is  furnished  inside  with  a 
number  of  radial  ribs  to  keep  the  fettling  in  place,  and 
when  in  position  is  geared  so  that  it  can  be  rotated  round  a 
horizontal  axis.  The  foundation  of  the  bed  consists  of  a 
moistened  mixture  of  non-siliceous  ore  and  lime  plastered 
on  and  then  well  dried  ;  and  the  working  surface  is  made  by 
melting  on  to  this  a  mixture  of  hammer  slag  and  ore,  and 
then  throwing  in  lumps  of  refractory  ore  to  roughen  it.  The 
grate  has  a  closed  ashpit,  and  the  air  for  the  combustion  of 
the  coal  is  blown  into  the  ashpit  under  a  light  pressure, 
and  also  in  jets  over  the  top  of  the  fuel  in  the  grate.  The 
draught  can  thus  be  controlled,  and  the  flame  varied  as 
desired.  The  other  end  of  the  cylinder  is  fitted  with  a 
movable  flue-piece,  that  can  be  pushed  back  when  a  charge 
is  to  be  introduced  or  withdrawn.  The  smaller  furnaces 
were  designed  to  work  a  charge  of  from  five  cwts.  to  six  cwts. 
of  solid  pig  with  the  usual  fettling,  but  in  the  larger  furnaces 
a  ton  of  pig  iron  melted  in  a  cupola  and  transferred  to  the 
cylinder  together  with  the  necessary  fettling  of  rich  ores  and 


136 


IEON  AND   STEEL. 


best  tap  cinder  can  be  worked  through  in  about  thirty 
minutes.  The  molten  pig  and  fettling  are  well  mixed 
together  by  the  revolution  of  the  bed,  and  the  refining  is 
very  rapid.  The  fluid  cinder  is  tapped  from  the  flue  end, 
and  the  puddled  ball  removed  through  the  flue  opening, 
very  large  apparatus  being  required  to  handle  it  and  to 
work  it  up  on  account  of  its  size.  The  cost  of  repairs  in 
this  furnace  is  very  heavy,  but  in  spite  of  this  it  was  very 
largely  used  in  America  for  many  years,  due  principally  to 
the  high  price  of  labour  in  that  country;  but  in  England, 
with  cheaper  labour,  it  did  not  pay, 
and  was  used  only  to  a  limited  extent. 
The  Pernot  Furnace. — The  bed  of 
this  furnace  consists  of  a  shallow 
circular  iron  pan  formed  of  segments 
riveted  together.  At  the  centre,  and 
underneath,  a  short  shaft  is  fixed  at 
right  angles  to  the  surface,  and  the 
whole  is  fitted  to  a  circular  trolley, 
so  that  the  bed  slopes  at  an  angle 
of  6°  from  the  horizontal.  The 

upper  surface  of  the  trolley  slopes  at  the  same  angle  as 
the  bed,  and  is,  therefore,  parallel  with  it.  A  number 
of  rollers  connected  with  the  bottom  of  the  bed  are  made 
to  run  in  a  channel  round  the  circumference  of  the 
trolley,  and  help  to  support  the  bed  while  allowing  it 
freedom  of  motion  round  the  central  driving  shaft.  The 
trolley  carrying  the  bed  is  run  in  through  a  gap  in  the 
furnace  at  the  back  and  brought  into  position  under  the 
roof,  and-  between  the  fire  bridge  and  the  flue  bridge. 
When  in  place,  the  lowest  part  of  the  bed  is  directly  under 
the  working  door  on  the  other  side  of  the  furnace.  If  a 
new  bed  has  just  been  put  in,  the  central  shaft  is  connected 
with  the  driving  gear,  consisting  of  a  worm  and  worm 
wheel  driven  by  a  small  engine,  and  the  working  bottom 


FIG.    24.— The     Pernot 
Furnace. 


THE   REFINING   OF   PIG  IEON  IN  SMALL   CHARGES.     137 

is  made  up  of  iron  ore  and  tap  cinder  melted  on  and  levelled 
by  the  aid  of  the  rotating  shell.  The  prepared  bed  may  be 
described  as  a  shallow  basin  sloped  so  that  molten  matter 
will  run  down  and  collect  in  one  part.  The  charge  of  pig 
iron  (15  cwts.  to  20cwts.)  is  introduced  with  the  fettling  and 
melted.  The  bed  is  then  rotated  at  the  rate  of  three 
revolutions  per  minute.  In  this  way  the  fettling  on  the 
upper  part  of  the  bed  is  oxidised  by  exposure  to  the  furnace 
gases,  and  is  then  carried  into  the  metal  on  the  lower  part 
of  the  bed,  there  to  exert  its  refining  influence,  and  then  to 
be  brought  out  again  by  the  motion  of  the  bed  to  absorb 
more  oxygen.  In  this  way  the  fettling  and  the  scrap,  which  is 
often  introduced,  acts  as  an  oxygen  carrier  to  the  impurities. 
The  rotation  of  the  bed  takes  the  place  of  the  rabbling  in 
the  hand-worked  furnace,  but  when  the  iron  has  come  to 
nature  the  balling  up  has  to  be  done  by  hand.  The  whole 
operation,  including  shingling,  occupies  about  two  hours. 
The  labour  required  is  the  same,  but  less  fatiguing,  and 
with  more  rapid  working  there  is  greater  economy  of  fuel. 
The  initial  cost  is  heavy,  and  the  wear  considerable.  The 
furnace  has  also  been  largely  used  for  steel  making,  which 
will  be  referred  to  later.  See  Fig.  24. 

Washed  Metal. — Sir  I.  L.  Bell  found  that  by  mixing  rich 
oxides  of  iron,  such  as  iron  ores,  hammer  scale,  etc.,  with 
molten  pig  iron  a  violent  reaction  is  set  up,  and  in  a  few 
minutes  practically  the  whole  of  the  silicon,  phosphorus, 
and  manganese  is  removed,  while  the  carbon  is  very  little 
affected.  If  then  the  refining  is  stopped  at  this  stage  a  very 
pure  white  cast  iron  is  obtained.  Krupp,  of  Essen,  used 
the  Pernot  furnace  fettled  with  rich  oxides  for  carrying  out 
the  process.  The  molten  pig  metal  is  brought  straight 
from  the  blast  furnace  and  run  on  to  the  bed  of  the  furnace, 
and  the  necessary  oxides  added.  In  from  five  to  ten  minutes 
there  is  a  sudden  evolution  of  carbon  monoxide,  when  the 
process  is  stopped  and  the  metal  tapped.  The  Americans 


138  IRON"   AND   STEEL. 

are  making  a  specially  pure  washed  metal  containing  only 
traces  of  silicon,  phosphorus,  manganese,  and  sulphur,  with 
3*25  per  cent,  of  carbon.  It  is  a  practically  pure  alloy  of 
iron  and  carbon. 

Gas  Furnaces  jor  Puddling. — A  number  of  furnaces  have 
been  designed  for  working  with  combustible  gas  instead  of 
coal,  and  the  most  successful  of  these  are  based  upon  the 
regenerative  principle  adopted  by  Siemens.  The  working 
of  a  charge  in  one  of  these  furnaces  is  much  the  same  as 
in  a  coal-fired  one,  and  the  method  of  using  the  gas  will  be 
made  clear  in  Chapter  VIII.  The  economy  of  gas  firing  was 
recognised  as  early  as  1855,  and  its  popularity  is  evidenced 
by  the  fact  that  the  gas  puddling  furnace,  under  various 
names,  has  been  largely  used  in  this  country,  on  the 
Continent,  and  in  America. 

Yorkshire  Bar  Iron. — The  best  quality  Yorkshire  bar 
has  long  been  noted  for  its  uniform  quality  and  excellence. 
That  made  at  the  Low  Moor  Works  is,  perhaps,  the  best 
known.  A  short  description  of  the  pig  iron  used  is  given 
on  p.  107.  The  pig  is  a  grey  or  strongly  mottled  iron, 
containing  about  3'5  per  cent,  of  carbon,  1  per  cent,  of 
silicon,  and  0*5  per  cent,  of  phosphorus.  It  is  first 
refined  in  a  refinery  similar  to  that  described  on  p.  120. 
In  this  process  nearly  all  the  silicon  and  the  greater  part 
of  the  phosphorus  is  removed  while  the  carbon  is  very 
little  affected,  owing,  no  doubt,  to  the  contact  of  the  metal 
with  the  coke  fuel  in  the  hearth.  The  charge  consists  of 
about  1J  tons  of  pigs  placed  on  a  bed  of  coke,  and  melted 
down  by  a  blast  driven  in  under  a  pressure  of  from  1J  Ibs. 
to  2  Ibs.  per  square  inch.  The  blast  is  directed  downwards 
into  the  bath  of  metal,  and  its  oxygen  oxidises  both 
impurities  and  metal.  Much  care  is  required  in  conducting 
this  refining,  and  in  judging  the  right  time  to  stop.  The 
metal  and  slag  are  tapped  into  a  shallow  iron  mould,  water 
thrown  on  to  the  mass  to  solidify  it,  and  the  slag  removed. 


THE   REFINING   OF   PIG   IRON  IN  SMALL   CHARGES.     UJ9 

The  plate  of  white  iron  thus  obtained  is  about  3  inches 
thick,  and  contains  all  its  carbon  in  the  combined  form. 
The  plate  is  broken  up,  and  the  iron  puddled ;  but  as  there 
is  very  little  silicon  and  phosphorus  to  be  removed  very 
little  fettling  is  required,  and  the  puddling  is  "  dry."  The 
puddling  furnace  in  which  the  process  is  carried  on  differs 
somewhat  from  the  ordinary  type.  At  the  flue  end  is  a 
heating  chamber  called  the  "  dandy,"  in  which  the  charge 
is  made  red  hot  by  the  furnace  gases  on  their  way  to  the 
flue.  The  bed  is  formed  of  iron  plates,  and  the  charge 
when  drawn  from  the  flue  at  a  red  heat  is  rapidly  worked 
upon  it.  The  metal  does  not  actually  melt,  but  remains  in 
a  pasty  state,  and  is  kept  at  a  welding  heat  while  the 
carbon  is  being  removed.  When  the  refining  is  finished 
the  mass  is  broken  up  into  a  number  of  balls,  which  are 
taken  to  the  hammer  to  be  shingled  into  "  noblins,"  about 
12  inches  square  and  2  inches  thick.  These  are  then 
broken  into  pieces,  and  sorted  according  to  their  fracture. 
The  pieces  are  then  piled,  re-heated  and  hammered  into 
billets,  which  are  again  re-heated  and  rolled  into  the 
required  form.  The  soft  fibrous  pieces  give  the  most 
malleable  bars. 

As  10  heats  of  about  3  cwt.  each  are  worked  off  in  12 
hours  the  process  is  very  rapid,  and  this  is  due  to  carbon 
only  having  to  be  removed  in  the  final  process. 


CHAPTEE  VI. 

CRUCIBLE    AND    WELD    STEEL. 

THE  general  effect  of  carbon  on  iron  would  be  noticed  at 
a  very  early  date,  as  it  is  absorbed  by  the  metal  at  a 
comparatively  low  temperature  in  sufficient  quantity  to 
influence  the  working  properties  of  the  metal.  But  although 
the  real  cause  of  the  useful  properties  of  ancient  steel  was 
not  known,  these  properties  were  taken  full  advantage  of 
in  the  manufacture  of  cutting  tools  and  weapons. 

Bergman  (1781)  was  the  first  to  trace  the  modification 
in  the  properties  of  iron  to  the  presence  of  variable  pro- 
portions of  carbon. 

The  ancient  term  steel  was  applied  to  the  variety  of  iron 
which  could  be  forged  and  welded  ;  hardened  and 
tempered  by  heating  and  sudden  cooling  ;  and  often  softened 
and  toughened  by  heating  and  slow  cooling.  Most  of  these 
properties  are  possessed  in  high  degree  by  iron  containing 
about  1  per  cent,  of  carbon.  As  the  percentage  of  carbon 
decreases  the  hardening  property  decreases,  and  below  0''2 
per  cent,  carbon  it  practically  disappears ;  but  as  the  carbon 
increases  the  forging  property  decreases,  and  in  the  neigh- 
bourhood of  2  per  cent,  of  carbon  disappears  altogether. 
Thus  there  are  limits  to  the  amount  of  carbon  permissible 
in  old-fashioned  steel,  and  the  various  authorities  are  not 
quite  in  agreement  with  regard  to  these  limits :  but  there 
are  a  number  of  well-known  grades  of  steel  suited  to 
different  uses,  and  these  will  be  noticed  later. 

The  modern  term  steel  has  a  much  wider  meaning,  and 
includes  not  only  true  steel,  but  also  a  number  of  alloys  of 


CEUCIBLE   AND   WELD   STEEL.  141 

iron  with  manganese,  nickel,  chromium,  tungsten,  vana- 
dium, and  similar  metals,  and  these  alloys  furnish  steels 
suited  to  a  large  variety  of  purposes.  It  is,  in  fact,  the 
adaptation  of  steel  to  modern  requirements. 

All  the  ancient  iron  and  steel  was  what  is  known  as 
weld  metal,  from  the  fact  that  it  was  produced  in  a  spongy 
state  and  then  hammered  to  weld  it  into  a  more  or  less 
homogeneous  mass.  Now,  by  far  the  greater  part  of  both 
iron  and  steel  is  finished  in  the  molten  state,  and  on  that 
account  is  called  ingot  metal.  The  following  is  a  general 
view  of  the  different  varieties  of  iron  and  steel  depending 
upon  the  percentage  of  carbon  present  :— 

Weld  Iron;  Ingot  Iron  Weld  Steel;  Ingot  Steel 

O'Oo  to'0'25  %  carbon  ()-25  to  f-8  %  carbon 

Cast  Iron  or  Pig  Iron 
1-8  to  4-3  %  carbon 

Weld  metal  always  contains  more  or  less  enclosed  slag, 
while  ingot  metal  is  quite  free  from  it. 

The  modifications  required  in  the  old  direct  processes  of 
extracting  iron  to  adapt  them  for  the  production  of  steel  may 
be  briefly  described  before  passing  on  to  the  more  modern 
methods  of  manufacture.  If  in  one  of  these  direct 
processes  the  operation  is  prolonged  so  as  to  leave  the 
reduced  metal  longer  in  contact  with  the  carbon  of  the 
fuel ;  and  if  the  cinder  is  not  too  basic  in  character,  or  is 
tapped  away  more  frequently  so  as  to  lessen  its  refining 
action,  the  reduced  metal  is  found  to  contain  carbon,  and 
the  finished  metal  possesses  the  ordinary  properties  of  steel. 
The  prolongation  of  the  smelting  is  brought  about  by 
altering  the  inclination  of  the  twyer  so  as  to  cause  it  to 
blow  more  across  the  hearth  than  into  it. 

Steel  may  also  be  made  by  the  puddling  process,  for  if 
the  pig  iron  contains  sufficient  manganese  to  act  as  a  cover 
for  the  carbon,  and  so  prevent  its  too  rapid  removal,  and  if 


142 


IRON   AND    STEEL. 


the  finishing  temperature  is  kept  lower  than  for  iron,  the 
metal  on  coming  to  nature  will  contain  carbon.  But  the 
process  is  not  sufficiently  under  control  to  furnish  a 
uniform  product. 

The   Cementation   Process. — High- class  carbon  steel,    or 
best    tool    steel,    is  made  in   this  country  from  the  finest 

qualities  of  bar  iron,  and  either 
Swedish,  Russian,  or  Yorkshire  weld 
iron  is  preferred.  For  high  grade 
cast  steel  best  Swedish  hammered 
bar  iron,  made  by  the  Walloon 
process  in  a  small  open  hearth, 
is  generally  used.  The  bars  are 
first  caused  to  absorb  carbon  by 
surrounding  them  with  charcoal, 
and  then  subjecting  them  to  pro- 
longed heating  at  a  uniform  tem- 
perature until  the  metal  has  taken 
up  sufficient  carbon  to  convert  it 
into  steel.  The  process  is  called 
cementation,  and  is  carried  on  in 
the  cementation  furnace  (Fig  25). 
The  firebrick  boxes  A,  A,  about  4  ft. 
by  4  ft.  by  12  ft.,  are  built  on  each 
side  of  a  fire  grate  B,  running  the 
full  length  of  the  furnace,  and  are 
arranged  so  that  the  flame  from 
the  grate  can  circulate  completely 
round  them,  and  heat  them  uniformly.  The  heating 
chamber  is  rectangular,  and  has  an  arched  roof  C, 
sufficiently  above  the  tops  of  the  boxes  to  allow  room  for 
the  workmen  to  charge  and  discharge  them.  Six  flues, 
C,  C,  three  on  each  side,  pass  through  the  roof  D,  where  it 
springs  from  the  side  walls,  into  a  conical  chimney,  which 
carries  off  tbe  products  of  combustion,  and  also  prevents 


FIG. 


25.  --  Cementation 
Furnace. 


CEUOIBLE  AND   WELD   STEEL.  143 

loss  of  heat  by  radiation  from  the  arched  roof.  The  grate 
is  fired  through  doors  at  both  ends. 

The  bars  for  conversion  are  usually  8  inches  wide,  f  inch 
thick,  and  12  feet  long.  A  layer  of  crushed  charcoal  freed 
from  dust  by  screening,  part  new  and  part  from  a  previous 
operation,  is  placed  on  the  bottom  of  the  box ;  then  a  layer 
of  bars  with  narrow  spaces  between  them,  then  another 
layer  of  charcoal,  and  so  on  until  the  box  is  completely 
filled.  Each  box  holds  about  12  tons  of  bars.  The  top  is 
then  covered  over  with  a  layer  of  moist  swarf  from  the 
grinding  troughs,  which  forms  a  good  tight  cover  to  protect 
the  contents  of  the  boxes  from  the  action  of  the  furnace 
gases.  A  trial  bar  is  left  protruding  through  a  rectangular 
slot  in  the  end  of  each  box,  through  which  it  can  be  with- 
drawn from  time  to  time  for  examination.  It  is  luted 
round  with  clay,  where  it  protrudes  from  the  box,  to  pre- 
vent the  admission  of  air.  The  firing  is  then  commenced, 
and  in  two  days  the  boxes  are  at  a  uniform  temperature, 
and  the  cementation  is  proceeding  regularly.  The  length 
of  time  required  to  complete  the  firing  depends  upon  the 
amount  of  carbon  to  be  absorbed,  but  the  quantity 
absorbed  also  depends  upon  the  temperature.  The 
maximum  for  800°  C.  appears  to  be  about  O9  per  cent, 
carbon,  and  increases  with  the  temperature.  The  tempera- 
ture usually  obtained  is  about  1000°  C.,  and  this  is  kept  up 
for  from  eight  to  eleven  days,  depending  upon  whether 
mild,  medium,  or  hard  steel  is  required.  About  twelve  tons 
of  coal  are  burnt  in  the  firing.  The  technical  terms  for  the 
duration  of  the  heats  are  spring,  country,  shear,  double 
shear,  and  steel  through  heat.  The  furnace  takes  about 
six  days  to  cool  down  after  the  firing  is  stopped  before  the 
workmen  can  enter  to  take  out  the  cemented  bars. 

The  converted  bars,  which  are  known  as  "  blister  bars," 
on  account  of  their  blistered  appearance,  are  broken  into 
short  lengths,  and  sorted  into  grades  by  an  expert.  The 


144  IKON   AND    STEEL. 

blisters  are  said  to  be  caused  by  the  reducing  action  of 
carbon  on  the  enclosed  slag,  resulting  in  the  formation 
of  carbon  monoxide,  which,  accumulating  in  the  neighbour- 
hood of  the  slag  patches  in  larger  quantities  than  will 
dissolve,  raises  the  pasty  metal  above  the  general  surface 
of  the  bar,  and  so  causes  the  blister.  This  explanation  was 
suggested  and  then  proved  by  Dr.  Percy ;  and  it  is  now 
well  known  that  mild  steel  that  has  been  melted,  and, 
therefore,  freed  from  slag,  can  be  cemented  without  the 
formation  of  blisters. 

During  cementation  carbon  slowly  penetrates  the  bar 
from  outside  towards  the  centre,  and  appears  to  do  so  by  a 
true  diffusion  process.  On  examining  the  fractured  surface 
of  a  bar  at  different  stages  the  shell  of  converted  metal  is 
seen  to  encroach  from  all  sides  on  the  iron  core,  which 
finally  disappears  in  the  steel  through  heat.  Koberts- 
Austen  heated  iron  with  diamond  dust  under  conditions  in 
which  no  gaseous  matter  could  possibly  take  part,  and 
found  that  carbon  was  absorbed  into  the  metal.  Abel 
clamped  together  accurately  planed  slabs  of  steel  and  iron, 
and  after  heating  them  to  a  bright  red  heat  for  several 
hours  found  that  carbon  had  passed  from  the  steel  to  the 
iron.  Bell  made  a  similar  experiment  with  wrought 
and  cast  iron,  and  proved  that  the  carbon  in  the  wrought 
iron  increased  from  0'04  to  0*4  per  cent.  In  the  Harvey 
process  for  the  cementation  of  armour  plates,  the  absorp- 
tion of  carbon  is  found  to  follow  the  ordinary  law  of 
diffusion.  But  under  the  conditions  that  obtain  in  the 
cementation  boxes  it  is  probable  that  gaseous  compounds 
of  carbon  also  play  an  important  part.  The  oxygen  of  the 
enclosed  air  would  form  carbon  monoxide,  CO,  which  is 
capable  of  diffusing  into  the  hot  iron,  and  would  then  give 
up  carbon  to  the  iron,  and  be  converted  into  carbon 
dioxide,  C02.  The  carbon  dioxide  thus  formed  would 
escape,  and  coming  into  contact  with  red-hot  carbon 


CEUCIBLE   AND   WELD   STEEL.  H,> 

on  the  outside  would  be  reconverted  into  carbon  monoxide. 
That  would  again  diffuse  into  the  bar,  and  thus  act  as  a 
carrier  of  carbon  to  the  metal.     Also  cyanogen  and  hydro- 
carbons,   usually   present,    would  probably  assist    in    the 
cementation.     The  action  is,  therefore,  a  complicated  one. 
Weld  Steel. — Before  Huntsman's  time  (1740)  the  blister 
bars  were  piled,   reheated,   and  hammered    or  rolled  into 
bars,  having  a  much  more  homogeneous  structure,  and  this 
piling,  reheating,  and  working  was  repeated  with  further 
improvement  in  the  quality  of  the  steel.     Even  now  this 
is  done  on  a  somewhat  limited  scale  for  the  production  of 
shear  steel   and  double  shear   steel  suitable  for  welding. 
But  steel  used  for  many  purposes  can  now  be  made  by  much 
cheaper  processes.     According  to  Dr.  Percy,   the  original 
process  consisted  in  cutting  the  blister  bars  into  ten-inch 
lengths,  which  were  then  raised  to  a  red  heat  and  drawn 
out    under    the    hammer    into    longer    and   thinner  bars. 
Several  of  these  were  then  made  into  a  pile,  one  end  of 
which  was  gripped  by  a  holder,  and  dusted  over  with  a 
mixture  of  clay  and  borax  to  prevent  oxidation.      The  pile 
was  then  reheated  in  a  hollow  fire,  hammered  down,  turned 
in  the  holder,  the  other  end  reheated  and  hammered.    This 
formed  a  bar  of  single  shear  steel ;  and  if  it  was  cut  into  two, 
the  two  halves  put  together,  reheated,  and  again  hammered 
into  a  single  bar,  this  formed  the  double  shear  steel.      The 
finer  varieties  of  steel  were  imported  from  Germany. 

Crucible  or  Cast  Steel.  —  Huntsman,  a  clockmaker  of 
Doncaster,  succeeded  in  melting  blister  steel  in  a  crucible 
and  casting  it  into  an  ingot,  by  which  metal  quite  free  from 
slag,  and  practically  homogeneous,  was  obtained.  He 
removed  to  Sheffield,  which  soon  became  the  home  of  the 
crucible  steel  process,  and  has  remained  so  to  the  present 
day.  It  is  carried  on  there  in  many  large  and  small  works, 
and  produces  steel  second  to  none  for  the  purposes  to  which 
it  is  suited. 

I.S.  L 


146 


IEOX   AND    STEEL. 


Steel  melting  crucibles  are  made  from  a  carefully  selected 
mixture  of  fireclays  with  a  little  coke  dust  added.  They 
are  18  inches  high  and  7  inches  wide  at  the  top.  Each 
crucible  has  a  hole  in  the  bottom,  and  is  provided  with  a 
circular  stand  of  the  same  diameter  as  the  bottom.  A 
closely  fitting  cover  with  a  circular  hole  in  the  centre, 
through  which  an  iron  rod  can  be  passed,  is  put  on  when 
the  crucible  is  in  position.  The  crucibles  are  carefully 

dried  and  heated  to  a  red  heat 
before  use.  Plumbago  crucibles 
are  sometimes  used,  and  are 
more  durable  than  the  clay  ones, 
but  there  is  more  risk  of  too 
much  silicon  being  reduced  and 
passing  into  the  metal.  The 
melting  is  preferably  carried  on 
in  a  wind  furnace  (Fig.  26), 
using  coke  for  fuel  ;  although 
gas  furnaces  of  the  Siemens 
regenerative  type  have  been  used, 
and  oil  furnaces  have  received 
some  attention.  But  steel  melters 
say  that  they  get  the  best  results 
in  a  coke  fired  furnace. 

Each  furnace  or  "hole"  is 
oval  in  shape,  and  will  take  two 
pots  side  by  side  with  room  around  them  for  the  fuel. 
It  is  lined  by  putting  a  wooden  core  of  the  proper  internal 
dimensions  on  the  grate  bars  and  then  ramming  moistened 
ganister  round  it.  When  the  core  is  removed  and  the 
ganisterwell  set  a  very  satisfactory  lining  is  formed.  When 
a  new  pot  is  used  it  is  placed  on  its  stand  in  the  furnace,  a 
handful  of  silica  sand  thrown  in  to  fill  up  the  hole,  and  the 
fire  made  up.  When  the  crucible  is  hot  enough  a  charge 
of  50  pounds  of  blister  steel  in  small  pieces  is  emptied  in 


FIG.  26. — Crucible  Furnace. 

A,  Furnace.      /?,  Annealing 

oven.     C,  Chimney. 


CEUCIBLE  AND   WELD   STEEL.  147 

through  a  sheet  iron  funnel,  and  the  cover  put  on.  It 
gradually  melts,  and  when  "killed"  is  ready  to  pour. 
Considerable  experience  is  required  to  judge  when  the 
metal  is  in  the  right  condition  for  pouring ;  for  if  it  has 
not  been  in  the  fire  long  enough  it  will  teem  "fiery"  and 
the  ingot  will  be  full  of  blow-holes,  and  if  too  long 
it  will  teem  "dead,"  and  the  ingot,  although  sound, will  be 
brittle  and  unworkable.  When  the  metal  is  properly 
"killed"  the  ingot  will  be  quite  sound  except  for  the 
usual  "pipe"  at  the  top.  The  killing  is  probably  due  to 
the  reduction  of  silicon  from  the  silica  in  the  walls  of  the 
pot,  and  its  passage  into  the  steel.  Silicon  is  said  to 
increase  the  solvent  power  of  the  metal  for  gases,  and  so 
produce  a  sound  casting.  If  too  much  silicon  is  reduced 
and  passes  into  the  metal  it  teems  dead. 

When  the  metal  has  been  poured  there  is  a  well-defined 
slag  line  round  the  inside  of  the  pot  where  corrosion  has 
taken  place  at  the  surface  of  the  molten  charge.  The 
second  charge,  therefore,  consists  of  44  Ibs.  of  blister  steel, 
and  the  final  charge  of  38  Ibs.  Each  crucible  is  used  for 
three  heats  under  normal  conditions. 

The  iron  moulds  are  usually  square,  in  cross-section, 
and  produce  an  ingot  about  3  inches  wide.  They  are  made 
in  two  parts,  which  are  clamped  together  after  the  whole 
surface  with  which  the  molten  metal  comes  into  contact  has 
been  reeked  with  the  smoke  from  burning  tar. 

The  teeming,  as  the  pouring  of  the  metal  into  the  mould 
is  called,  must  be  done  very  carefully  and  at  the  right  time 
if  a  sound  ingot  is  to  be  obtained.  The  ingot  mould  is 
placed  in  a  slightly  inclined  position  to  receive  the  metal, 
which  is  poured  down  the  centre  of  the  mould  in  as  thin  a 
stream  as  possible.  The  small  cross-section  favours  rapid 
cooling,  and  the  slow  pouring  allows  the  solidifying  metal 
to  follow  up  the  incoming  fluid,  so  that  the  structure  of  the 
ingot  when  cold  is  uniform,  and  the  pipe  at  the  top  is 

L2 


148 


IEON   AND   STEEL. 


CKUCIBLE   AND   WELD   STEEL.  149 

reduced  to  a  minimum.  The  presence  of  the  pipe  is  an 
indication  of  sound  metal.  There  is  always  a  certain 
amount  of  waste,  for  the  ingots  have  to  be  "  topped,"  that 
is,  the  piped  portion  cut  off.  This  is  generally  about  10  per 
cent,  of  the  whole. 

The  melting  down  of  carefully- selected  blister  bars  is 
without  doubt  an  ideal  method  for  making  the  highest 
grade  crucible  steel ;  but  cast  steel  is  also  made  from  bar 
iron  without  cementing  it.  For  this  purpose  the  bars  are 
sheared  into  short  lengths,  and  charged  into  the  crucible 
together  with  a  calculated  quantity  of  charcoal  to  bring  the 
metal  up  to  the  required  content  of  carbon.  The  melter 
knows  from  experience  what  proportion  of  the  added  carbon 
will  pass  into  the  metal,  and  makes  his  calculations 
accordingly.  A  little  spiegeleisen  is  added  when  the  charge 
is  melted,  as  it  is  found  to  improve  the  quality  of  the  steel. 
This  method  is  largely  employed  in  America,  where 
cemented  bars  do  not  appear  to  be  made. 

The  melting  down  of  proportioned  charges  of  blister 
steel  and  unconverted  bar  or  good  quality  scrap  is  largely 
followed,  and  forms  a  very  useful  general  method.  The 
method  of  making  an  inferior  quality  of  cast  steel  by 
melting  bar  iron  with  charcoal  and  black  oxide  of  man- 
ganese was  used  by  Mushet  as  early  as  1801.  J.  M.  Heath 
strongly  heated  a  mixture  of  the  black  oxide  and  coal  tar  in 
a  crucible,  and  added  the  resulting  carbide  of  manganese 
to  the  charge  of  British  bar  iron  and  charcoal.  He  thus 
produced  a  moderately  good  steel  from  inferior  bar  iron. 

Pure  white  pig  iron  may  be  melted  down  with  good  mild 
scrap  or  bar  iron.  The  carbon  of  the  pig  is  disseminated 
through  the  whole  charge,  and  thus  brought  down.  Either 
Swedish  white  pig  iron  or  good  "  washed  "  metal  may  be 
used.  Also  it  is  probable  that  much  good  open  hearth  and 
Bessemer  scrap  is  used  in  crucible  steel  manufacture. 

When  special  tool  steels  are  being  made  the  calculated 


150 


IKON  AND   STEEL. 


proportion  of  the  iron  alloy,  ferro-tungsten,  ferro-chrome, 
etc.,  is  added  to  the  crucible  charge,  and  when  properly 
melted  the  resulting  steel  is  teemed  into  the  moulds  in 
the  usual  manner. 

It  is  not  often  that  crucible  steel  containing  less  than  0*5 
per  cent,  of  carbon  is  made  unless  for  special  purposes. 

Generally  the  range  is  from 
0'5  per  cent,  to  1*8  per  cent., 
although  more  carbon  can 
be  introduced.  But  these 
high  carbon  steels  are  very 
difficult  to  manipulate,  and 
are  only  used  for  special 
work.  A  good  general  view 
of  a  steel  melting  shop  is 
shown  in  Fig.  27.  The 
melting  holes  are  on  the 
right,  nearly  level  with  the 
floor,  and  there  are  no  less 
than  100  of  them  in  the 
complete  shop. 

Styrian  Steel— The  Erz- 
berg,  or   ore  mountain,  in 
Styria    furnishes    a    good 
spathic  ore,  from  which  a 
very   pure    white    iron    is 
obtained,  and  this  metal  is 
converted  into  steel  of  ex- 
finery,   which  is   shown    in 
A,    is   rectangular   in 


FIG.  28. — Styrian  Open  Hearth. 


cellent    quality  in  a  charcoal 

section   in  Fig.    28.      The   hearth, 

plan,  and   is   about  30  inches   long  by   20   inches   wide. 

The  sides  are  formed  of  cast  iron  plates  inclined  at  a  small 

angle,  and  the  bottom,  or  sole,  is  lined  with  a  brasque  of 

charcoal  and  slag  well  stamped  in.     The  blast,   which  is 

supplied  through   an  inclined  twyer,  B,  at  a  pressure  of 


CRUCIBLE   AND   WELD   STEEL.  151 

|  Ib.  on  the  square  inch,  is  heated  by  being  driven  through 
a  hot  iron  pipe  b,  before  entering  the  hearth.  This  pipe 
passes  to  and  fro  through  the  chimney,  D,  where  it  is 
heated  by  the  waste  heat  of  the  gases  escaping  from  the 
hearth  through  C,  and  the  temperature  of  the  blast  is  thus 
raised  to  160°  C.  The  tall  wide  chimney  is  necessary  to 
prevent  the  escape  of  sparks  into  the  open  air,  as  the 
buildings  round  the  works  are  largely  constructed  of  wood, 
and  thus  liable  to  take  fire.  The  hearth  is  supplied  with 
charcoal  fuel,  and  when  in  working  order  a  pile  of  pieces  of 
white  iron  weighing  about  130  Ibs.  gripped  in  a  pair  of  tongs 
is  brought  into  the  hearth  and  held  over  the  glowing  charcoal, 
but  not  in  the  blast.  It  is  balanced  by  a  weight  hung  on 
the  shanks  of  the  tongs,  the  edge  of  the  side  plate  acting  as 
a  fulcrum.  It  is  thus  gradually  heated,  and  when 
uniformly  hot  a  second  pile  of  88  Ibs.  is  placed  in  the 
hearth,  and  the  first  one  brought  over  the  twyer.  During 
the  heating  the  metal  is  freely  sprinkled  with  slag.  The 
two  piles  are  then  melted  one  after  the  other,  and  run  down 
into  the  hearth.  The  slag  is  tapped  at  once,  the  blast 
reduced,  and  a  shovelful  of  wet  slag  thrown  on  to  the 
metal,  which  then  becomes  pasty  and  can  be  raised  in  the 
hearth.  The  pasty  mass  is  allowed  to  remain  for  a  few 
minutes  to  cool  to  the  proper  temperature  for  hammering, 
when  it  is  taken  to  the  hammer  and  divided  up  into  12 
slabs  or  "  massel,"  which  are  then  ready  for  reheating  and 
welding.  These  massel  are  made  into  piles  to  be  held  in 
tongs  and  reheated  as  occasion  offers  in  the  same  hearth 
as  the  refining  is  carried  on.  The  various  piles  in  the 
hearth  are  moved  about  as  required. 

About  2  cwt.  of  white  iron  is  refined  at  one  operation 
lasting  about  3  hours.  The  loss  is  about  10  per  cent,  of 
the  metal  charged  in.  It  is  said  that  a  skilful  operator 
can  produce  refined  metal  varying  from  the  purest  iron  to 
the  hardest  tool  steel  at  will. 


152 


IEON  AND   STEEL. 


The  reheated  piles  are  drawn  out  into  bars  under  the 
hammer,  quenched  in  water,  broken  into  short  pieces,  and 
sorted.  An  expert  sorter  can  judge  the  content  of  carbon 
very  accurately  by  the  appearance  of  the  fractured  surface. 
Formerly  the  crude  metal  thus  obtained  was  cemented  by 
further  heating  with  charcoal,  and  finished  as  weld  steel ; 
but  now  the  sorted  pieces  are  melted  in  graphite  crucibles 
for  the  production  of  cast  steel,  as  in  the  case  of  cemented 
bars.  The  composition  of  the  cast  iron  used  and  the  steel 
obtained  is  shown  below7:  — 


Carbon. 

Silicon. 

Manganese. 

Phosphorus. 

Sulphm- 

White  Cast  Iron  . 

3-430 

0-110 

1-010 

0-066 

0-01  fi 

Crucible  Steel 

1-020 

0-020 

0-043 

0-019 

O'OOS 

A  glance  at  the  composition  of  the  cast  iron  shows  that 
the  changes  taking  place  during  the  refining  process  are 
simple  in  character.  Only  small  quantities  of  silicon, 
phosphorus  and  sulphur  have  to  be  eliminated,  and  there 
is  sufficient  manganese  to  act  as  a  cover  for  the  carbon 
while  they  are  being  sufficiently  removed  to  produce  high- 
class  metal.  Carbon  can  thus  be  kept  in  the  charge  until 
the  refining  is  finished.  No  working  up  in  front  of  the 
twyer,  as  was  necessary  in  the  old  fineries,  is  required. 
The  cinder  contains  oxide  of  manganese,  which  renders  it 
more  fluid  and  less  oxidising  than  ordinary  cinder,  and  so 
protects  the  "young"  steel  as  it  comes  to  nature.  With 
the  more  impure  pig  worked  in  this  country  it  is  necessary 
to  remove  practically  the  whole  of  the  carbon  in  order  that 
the  impurities  may  be  sufficiently  eliminated. 

The  Styrian  process  does  not  depend  for  its  success  so 
much  upon  skill  in  working  as  upon  locality.  The  districts 
in  which  the  process  is  carried  on  are  densely  wooded,  and 


CBUCIBLE  AND   WELD   STEEL.  153 

abundant  supplies  of  charcoal  can  be  obtained.  This  is 
used  both  for  smelting  the  local  ores  and  for  the  refining 
process.  Some  55  bushels  of  pine  charcoal  are  used  in 
producing  2  cwts.  of  steel.  It  is  only  in  such  countries  as 
Styria  and  Sweden  that  these  processes  can  be  made  a 
commercial  success.  Another  point  of  importance  is  that 
the  country  is  hilly,  and  water  power  is  sufficiently  abun- 
dant to  enable  the  mechanical  operations  to  be  carried  on 
by  the  power  derived  from  turbines  and  water-wheels. 
Thus  the  tilt  hammers  used  in  working  the  refined  metal 
into  bars  are  actuated  by  water  power. 

While  the  pure  white  iron  is  the  principal  product  of 
Styrian  blast  furnaces,  both  grey  pig  and  spiegeleisen  are 
made.  Also  the  puddling  furnace  and  the  Siemens  open 
hearth  are  found  working  side  by  side  with  the  primitive 
fineries  ;  but  the  steel  they  produce  is  only  mild  or  middling 
hard  in  character.  Styrian  steel,  however,  has  long  been 
noted,  and  still  holds  its  own,  for  an  excellence  of  quality 
probably  second  to  none. 

Case  Hardening. — It  is  often  necessary  that  a  tool  or 
part  of  a  machine  should  possess  a  moderately  soft  and 
tough  core  with  a  hard  resisting  surface.  It  is  then  usual 
to  resort  to  a  partial  cementation,  and  the  process  of  case 
hardening  is  carried  out.  This  consists  in  heating  the 
finished  machine  parts  or  tools  to  a  sufficient  temperature 
in  contact  with  carbonaceous  matter.  This  is  usually 
either  wood  charcoal  or  animal  charcoal  obtained  by 
charring  leather  scrap.  When  a  large  number  of  articles 
are  to  be  treated,  they  are  packed  in  an  iron  box  with  the 
cement  powder,  and  heated  to  the  proper  temperature  in  a 
muffle  or  reverberatory  furnace.  Care  is  taken  to  exclude 
air  by  a  well-fitting  lid ;  and  the  duration  of  the  heating 
depends  upon  the  thickness  of  the  case  or  shell  of  cement 
steel  to  be  formed.  A  shell  about  J  inch  thick  is  formed  in 
about  four  hours.  The  articles  are  then  plunged  into 


154  IEON  AND   STEEL. 

water  while  red  hot  to  harden  the  surface.  Care  must  be 
taken  that  the  quenching  is  sufficiently  rapid  and  uniform 
for  the  whole  charge,  if  good  results  are  to  he  obtained.  As 
the  point  of  saturation  depends  upon  the  temperature,  this 
must  be  carefully  regulated,  or  the  shell  will  be  too  hard  or 
too  soft  for  the  purpose.  Many  case  hardeners  are  now 
using  pyrometers  with  their  furnaces  in  order  to  better 
control  their  working.  Also  the  success  of  the  process 
depends  largely  upon  the  condition  of  the  uncemented  core 
or  sap  of  the  piece  when  the  shell  is  hardened.  Now  this 
core  is  not  always  in  the  best  condition  for  the  purpose 
when  the  hardening  is  effected  straight  from  the  cementing 
vessel ;  so  that  it  is  preferable  to  allow  the  articles  to  cool  in 
the  vessel,  and  to  re-heat  them  rapidly  to  a  red  heat  for 
hardening  in  the  ordinary  way.  This  is  more  trouble,  but 
a  better  and  more  uniform  result  is  obtained.  When  a  few 
small  articles  are  to  be  case  hardened  they  are  heated, 
dipped  in  yellow  prussiate  of  potash  (rLiFeCeNe),  which 
supplies  the  carbon,  re-heated,  and  plunged  into  water  to 
harden  the  surface.  Various  preparations  are  sold  for  the 
purpose,  but  they  all  act  in  the  same  way  by  giving  up 
carbon  to  the  hot  metal. 

The  Harvey  Process  for  cementing  one  side  of  large  mild 
steel  armour  plates  containing  up  to  0*35  per  cent,  of 
carbon  is  carried  on  in  regenerative  gas  furnaces.  The  bed 
of  the  furnace  is  movable,  and  consists  of  a  trolley  that  can 
be  run  in  and  out  at  will.  The  bottom  of  the  trolley  is 
covered  with  a  thick  layer  of  fire  bricks,  in  the  upper  part 
of  which  flues  are  constructed  for  the  circulation  of  hot 
gases;  and  upon  this  a  layer  of  fireclay  is  formed. 
The  plate  to  be  cemented  is  placed  on  the  clay,  and 
covered  with  a  layer  of  charcoal.  On  the  top  of  this 
another  plate  is  placed,  and  covered  with  a  layer  of 
sand.  Another  layer  of  firebrick  is  arranged  on  the 
top  of  the  sand  to  form  a  protective  covering.  The 


CRUCIBLE  AND  WELD   STEEL. 


155 


trolley  thus  prepared  is  brought  into  position  under  the 
roof  of  the  furnace.  The  end  doors,  which  are  cast-iron 
frames  filled  in  with  fire  bricks,  are  closed,  and  the  firing 
is  commenced.  The  carbon  diffuses  downwards  into  the 
bottom  plate,  and  upwards  into  the  top  plate,  and  the 
amount  absorbed  depends  upon  the  temperature  of  the 
furnace  and  the  duration  of  the  process.  This  may  extend 
from  five  to  fourteen  days.  The  trolley  is  moved  in  and  out 
of  the  furnace  by  an  endless  chain,  and  the  wheels  and 
gearing  generally  are  far  enough  removed  from  the  working 
bottom  to  prevent  their  being  damaged  by  the  heat. 

The  surface  layer  of  the  cemented  plate  may  contain  as 
much  as  T35  per  cent,  of  carbon ;  but  in  the  inner  layers 
the  percentage  of  carbon  gradually  diminishes  to  the 
original  content,  say  0'35.  The  plates  are  several  tons  in 
weight,  and  usually  about  10  inches  thick. 

When  the  plates  have  cooled  down  sufficiently,  they  are 
machined  and  shaped,  if  necessary.  Then  they  are 
re-heated  to  a  cherry  red  heat  in  a  special  trolley  furnace, 
and  hardened  by  quenching  with  a  water  spray.  This  portion 
of  the  work  must  be  carefully  done,  if  the  surface  is  to  have 
a  uniform  resistance. 

Some  of  the  uses  to  which  crucible  steel  is  put,  with 
the  approximate  amount  of  carbon  present,  are  indicated 
below : — 

Cutlery 

Chisels 

Dies 

Saws,  chisels 

Drills 

Shear  steel  is  largely  used  for  welding  to  iron  in  the 
manufacture  of  edge  tools  for  agricultural  and  other 
purposes. 


0-6  per  cent.  C. 

Taps  and  dies     . 

1-1  per  cent.  C. 

0-7 

Turning  tools     . 

1-2          ,, 

0-8 

Long  files  . 

1-3 

0-9 

Saw  files    . 

1'4          ,, 

i-o 

Eazors,  lancets  . 

1-5 

CHAPTEK  VII. 

THE    BESSEMER   PROCESS. 

THE  conversion  of  pig  iron  into  weld  iron  or  wrought  iron 
has  already  been  considered,  and  the  character  of  the 
changes  taking  place  explained  ;  so  that  the  consideration 
of  the  problem  of  converting  pig  iron  into  ingot  iron  and 
steel  will  not  present  any  difficulty.  The  silicon  and  carbon 
of  the  pig  must  be  as  completely  removed  in  the  case  of 
ingot  iron  as  in  the  case  of  weld  iron,  and  for  ingot  steel 
the  carbon  must  be  either  partially  removed,  or  completely 
removed,  and  then  sufficient  carbon  added  to  the  metal  in 
the  finishing  stage  to  bring  it  up  to  the  required  percentage. 
Also,  if  phosphorus  and  sulphur  are  present  in  notable 
quantities  they  must  be  brought  down,  as  in  the  case  of 
weld  irons,  so  as  not  to  interfere  with  the  working  properties 
of  the  metal.  The  presence  of  manganese  in  the  pig  metal 
presents  no  difficulty. 

In  puddling  and  finery  processes  the  removal  .of  the  non- 
metals  is  largely  effected  by  the  oxygen  in  basic  iron  cinders 
and  rich  oxides  of  iron.  But  there  is  no  reason  ^iy  the 
oxygen  of  the  air  should  not  be  directly  utilised  to  do  the 
work,  providing  the  necessary  conditions  can  be  com- 
plied with.  This  was  attempted  by  Bessemer  in  the  years 
preceding  1855,  in  which  year  he  took  out  a  patent  for  a 
process  that  has  developed  into  the  process  which  forms  the 
subject  of  this  chapter. 

It  is  a  far  cry  from  the  clay  crucible  with  its  charge  of  12 
pounds  of  pig  iron  melted  in  a  wind  furnace  to  the  modern 
vessel  with  its  charge  of  20  tons  of  molten  metal ;  and 


THE   BESSEMER   PROCESS.  157 

Bessemer  had  a  very  tedious  task  to  make  his  process  even 
a  partial  success. 

In  explaining  the  principles  of  the  process  it  will  be  best 
to  consider  the  treatment  of  a  non-phosphoric  pig  iron,  that 
is,  one  from  which  the  removal  of  silicon  and  carbon  only 
need  be  considered.  If  a  clay  pipe  is  thrust  to  the  bottom 
of  a  charge  of  such  metal  in  the  molten  state,  and  a  rapid 
current  of  air  driven  through  it,  the  silicon  will  burn  to 
silica,  much  heat  will  be  developed  by  its  combustion,  and 
the  temperature  of  the  metal  will  rise  rapidly.  When  the 
silicon  has  burnt  the  carbon  will  burn,  and  the  evolution  of 
heat  will  continue  until  the  carbon  has  all  disappeared. 
Now  this  internal  heat  is  developed  so  rapidly  that  the  rise 
in  temperature  of  the  mass  more  than  keeps  pace  with  the 
increase  in  the  melting  point  of  the  iron  as  it  refines  ;  so 
that  the  final  metal,  though  free  from  silicon  and  carbon 
and  with  a  melting  point  approaching  1600°  C.,  is  still  per- 
fectly fluid,  and  can  be  readily  cast  into  an  ingot.  But  it  is 
impossible  to  drive  air  through  the  metal  without  oxidising 
some  of  it  along  with  the  impurities,  and  the  oxide  thus 
formed,  in  part  at  least,  dissolves  in  the  molten  metal,  and 
gives  to  it  the  general  character  of  burnt  iron,  which  is 
unworkable.  This  was  Bessemer's  great  stumbling  block  ; 
he  could  remove  the  silicon  and  carbon,  but  his  refined  metal 
would  not  forge.  About  this  time  Mushet  was  using  man- 
ganese in  a  crucible  steel  process,  and  he  suggested  that  the 
addition  of  manganese  in  some  form  to  the  bath  of  molten 
refined  iron  would  remove  the  oxygen,  and  render  the  metal 
workable.  This  proved  to  be  the  solution  of  the  difficulty  ; 
and  in  practice  the  manganiferous  pig  iron  spiegdeisen  was 
found  to  be  a  suitable  medium  for  introducing  the  man- 
ganese. This,  however,  carried  carbon  into  the  charge,  and 
as  it  was  not  all  removed  subsequently,  iron  often  containing 
more  carbon  than  weld  iron  was  obtained,  and  to  this  the  term 
"  mild  steel  "  was  applied.  Now,  the  manufacture  of 


158  IEON  AND   STEEL. 

ferro-manganese  containing  as  much  as  80  per  cent,  of  man- 
ganese enables  a  much  smaller  quantity  to  be  used  in 
order  to  introduce  the  necessary  manganese,  and  as  the 
comparatively  small  amount  of  carbon  carried  in  with  it  is 
practically  all  oxidised,  ingot  iron  can  be  produced  at  will. 
It  may  be  remarked  in  this  connection  that  Styrian  and 
Swedish  pig  irons,  which  are  often  rich  in  manganese,  may 
produce  good  Bessemer  metal  without  the  addition  of  man- 
ganese, and  as  much  as  0'3  per  cent,  of  manganese  be  left 
in  the  steel. 

Part  of  the  oxide  of  iron  formed  while  the  air  is  being 
blown  through  the  molten  metal  combines  with  the  silica, 
and  a  slag  or  cinder  rich  in  silica  is  produced  ;  and  the  oxide 
of  manganese  formed  during  the  reduction  of  the  dissolved 
oxide  of  iron  by  the  added  manganese,  not  being  soluble  to 
the  fluid  metal,  passes  out  and  comes  into  contact  with  the 
siliceous  slag,  by  which  it  is  readily  taken  up.  The  man- 
ganese thus  acts  as  a  clearing  agent  by  removing  the  excess 
of  oxygen  and  giving  a  good  workable  metal. 

The  evolution  of  the  Bessemer  converter,  as  the  vessel  is 
called,  forms  a  very  interesting  part  of  the  modern  manufac- 
ture of  iron  and  steel,  and  is  one  of  the  best  examples  of 
difficulties  overcome  in  the  march  of  industrial  progress. 
Bessemer  himself  recognised  the  necessity  (a)  of  blowing 
vigorously  into  the  very  heart  of  the  metal ;  (b)  of  blowing 
only  when  the  whole  of  the  charge  was  in  the  vessel ;  and 
(c)  of  being  able  to  stop  or  resume  the  blowing  at  will. 
This  led  to  the  adoption  of  a  vessel  which  could  be  rotated 
on  an  axis,  and  to  blowing  through  the  bottom  of  the  vessel. 
But  there  are  still  some  moderately  successful,  fixed,  side- 
blown  vessels  in  use.  The  converting  vessel  has  undergone 
various  changes  both  in  size  and  shape  ;  and  several  modifi- 
cations of  the  simple  process  of  blowing  cold  air  through  the 
molten  metal  have  been  tried,  but  none  of  them  proved 
successful.  The  principal  are :  (1)  the  injection  of  finely 


THE    BESSEMER   PROCESS.  159 

divided  carbon  with  the  blast  to  effect  the  final  carburisation ; 
(2)  heating  the  blast  to  increase  the  temperature  ;  (3)  the 
blowing  in  of  air  and  steam  alternately  ;  (4)  blowing  with 
pure  oxygen  and  hydrocarbons  obtained  from  petroleum  to 
effect  the  expulsion  of  phosphorus  and  sulphur  at  very 
high  temperatures  in  a  reducing  atmosphere  of  hydrogen 
and  hydrocarbons. 

Among  the  early  successes  of  the  original  process  was  a 
simple  converter  worked  with  hand-gearing  that  turned  out 
ingots  of  good  metal  at  £18  per  ton. 

The  Acid  Bessemer  Process. — This  is  the  original  process 
in  which  the  molten  metal  is  always  in  contact  with  the 
highly  siliceous  lining  of  the  converting  vessel,  and  on  that 
account  the  slag  formed  is  highly  siliceous  or  "  acid  "  in 
character.  Hence  the  title  of  the  process,  which  is  suffi- 
ciently expressive.  On  account  of  the  acid  nature  of  the  slag, 
any  phosphorus  present  in  the  metal  at  the  beginning  of 
the  operation  is  still  there  at  the  end ;  for  the  character  of 
the  slag  prevents  any  phosphoric  oxide  formed  during  the 
blow  from  passing  into  it,  or  if  it  passes  into  the  slag  it  is 
eventually  reduced,  and  the  phosphorus  passes  back  into 
the  metal.  On  this  account  only  pig  iron  practically  free 
from  phosphorus  can  be  used.  This  has  created  a 
demand  for  a  pure  pig  iron  smelted  from  pure  haematite 
ores,  and  known  as  Bessemer  pig. 

The  Converter. — The  shape  of  the  vessel  has  varied  con- 
siderably during  its  evolution,  but  the  one  now  largely  used 
is  circular  in  horizontal  section,  and  symmetrical  with 
regard  to  its  vertical  axis.  It  is  known  as  the  concentric 
converter,  and  the  shell,  which  is  made  of  shaped  wrought 
iron  plates  one  inch  thick,  held  together  by  straps  and 
rivets,  takes  the  form  of  a  cylinder  with  a  conical  end. 
The  bottom  edge  of  the  cylinder,  which  projects  inwards,  is 
made  of  strong  angle  iron  to  act  as  a  support  for  the  lining. 
The  conical  end  forms  the  neck  of  the  vessel,  and  is  made 


160  IKON  AND   STEEL. 

separately,  so  that  it  can  be  detached  if  necessary.  Bound 
the  middle  of  the  cylindrical  portion  is  fixed  a  strong  steel 
belt,  from  the  ends  of  a  diameter  of  which  project  two 
trunnions  formed  of  cast  iron  box  sections.  The  trunnions 
are  supported  on  piers  between  which  the  vessel  can  be 
rotated  at  will.  The  rotation  may  be  effected  by  a  worm 
wheel  fixed  to  one  of  the  trunnions,  and  geared  to  a  screw 
which  is  worked  direct  from  the  cranks  of  a  pair  of  hydraulic 
engines  fixed  to  one  of  the  piers.  In  this  way  the  converter 
can  be  rotated  in  either  direction.  One  of  the  trunnions  is 
hollow,  and  is  connected  with  the  blast  main  by  a  telescope 
joint.  The  working  lining  is  made  of  ganister  (see  p.  46), 
which  is  moistened  with  water  to  make  it  bind,  and  then 
rammed  between  the  inside  of  the  shell  and  the  outside  of 
a  wooden  core,  the  space  between  the  two  forming  the 
thickness  of  the  lining.  The  neck  is  lined  in  the  same 
manner.  The  bottom,  which  is  also  made  separately, 
consists  of  a  strong  iron  frame  that  supports  the  refractory 
material  forming  the  working  bottom.  The  central  portion, 
which  is  usually  somewhat  raised  above  the  general  level, 
forms  the  twyer  region,  and  is  pierced  by  a  number  of 
slightly  conical  holes  opening  above  into  the  body  of  the 
vessel,  and  below  into  an  iron  box,  the  blast  chest.  The 
interior  of  this  chest  is  connected  directly  by  a  goose  neck 
with  the  hollow  trunnion  jointed  to  the  blast  main.  The 
twyers  are  slightly  tapered  fire  clay  cylinders,  each  of 
which  is  perforated  by  a  number  of  channels  H  inch  in 
diameter.  These  twyers  are  passed  through  holes  in  the 
bottom  plate  which  also  forms  the  top  plate  of  the  blast 
chest,  so  that  their  inner  ends  are  just  flush  with  the 
bottom.  They  are  held  in  position  by  eccentric  catches 
fitted  to  the  sides  of  the  holes  through  which  they  pass,  and 
the  ends  are  luted  round  with  clay.  The  number  of 
twyers  and  perforations  vary  according  to  the  size  of  the 
vessel,  but  10  twyers,  each  containing  10  channels,  may  be 


THE    BESSEMER   PROCESS. 


161 


taken  as  an  average,  which  would  represent  a  blast  opening 

into  the  converter  of  nearly  4  inches  diameter.  The  bottom 

plate  of  the  blast  chest,  although  quite  air-tight  when  in 

position,  is  easily  removed,    so    that    the   twyers    can  be 

examined  between  the  heats,   and    replaced  if  necessary. 

The  bottom  lining 

is  subjected  to  the 

principal      stress 

and     corrosive 

action     during 

working,      and 

must  be  replaced 

after  some  20  to 

30  heats,  while  the 

side    lining    will 

last  through  from 

400  to  500  heats 

under    normal 

conditions. 

The  bottom  is 
fixed  to  the  body 
of  the  converter 
by  cotters,  which 
are  readily  re- 
moved, and  the 
joint  where  the 
body  and  the 
bottom  meet  is 
made  tight  by 

ramming  in  a  mixture  of  moistened  ganister  and  clay.  There 
is  a  hydraulic  lift  directly  under  the  converter  when  it  is  in 
position,  on  to  which  a  trolley  can  be  run  to  be  lifted  into 
contact  with  the  bottom  when  it  has  to  be  repaired.  In  this 
way  an  old  bottom  can  be  readily  taken  away,  and  a  relined 
one  put  in  its  place.  The  general  form  of  the  concentric 

i.s,  M 


FIG.  29. — Concentric  Converter. 
A,  Body.  D,  Hollow  trunnion. 


B,  Bottom. 
(7,  Blast  chest. 


E,  Trolley. 


162 


IEON  AND   STEEL. 


[± 


/  x 

/ 


FIG.  30. — Eccentric  Converter. 


A,  Body. 

B,  Trunnion. 
c,  Bottom. 


D,  Trolley. 

E,  Blast  main. 

r,  Hydraulic  table. 


THE   BESSEMER   PEOCESS.  163 

converter,  and  the  method  of  connecting  the  bottom  with 
the  body  and  the  blast  main,  is  shown  in  Fig.  29. 

A  15-ton  converter  of  the  concentric  type  has  the  follow- 
ing dimensions  : — 24  feet  5  inches  high  and  10  feet 
5  inches  in  diameter  ;  it  is  mounted  on  standards  or  piers 
20  feet  high,  and  weighs  from  60  to  70  tons.  It  can  be 
moved  readily  into  various  positions  round  its  horizontal 
axis,  such  as  the  horizontal  when  charging,  the  vertical 
when  blowing,  and  the  more  or  less  inverted  when  running 
slag  or  metal,  or  for  tipping  out  residues.  It  can  also  be 
worked  from  both  sides  if  necessary. 

The  capacity  of  a  converter  depends  upon  the  width  of 
the  mouth ;  the  wider  the  moutli  the  smaller  the  capacity, 
for  the  whole  of  the  molten  charge  must  lie  in  the  vessel 
when  it  is  in  the  horizontal  position,  and  a  wide  mouth 
means  a  shallow  bath  of  metal,  and  consequently  a  small 
charge.  The  wider  the  mouth  the  less  the  waste  through 
ejectment,  as  the  ejected  metal  has  more  chance  of  falling- 
back  into  the  vessel ;  but  the  narrower  the  mouth  the 
higher  the  temperature  obtained  in  working,  and  the 
greater  the  back  pressure.  So  that  there  are  limits  to  the 
width  of  the  mouth,  and  these  can  only  be  determined  by 
practical  experience. 

In  converters  of  the  eccentric  type  the  axis  of  the  neck  is 
at  an  angle  of  about  30°  to  the  vertical  axis ;  this  increases 
the  capacity  of  the  converter,  as  the  belly  is  larger  ;  but 
there  is  no  chance  of  the  ejected  metal  falling  back,  and  the 
converter  can  be  worked  from  one  side  only.  In  Fig.  30  is 
shown  the  form  of  the  eccentric  converter,  and  the  hydraulic 
table  for  lifting  the  bottom  into  position. 

Bloiving  Engines. — The  blast  required  to  work  the  con- 
verter is  usually  supplied  by  a  double  cylinder  blowing 
engine  of  the  horizontal  type.  The  air  is  driven  into  a 
large  iron  reservoir  to  convert  the  pulse-like  flow  into  a 
steady  one,  and  leaves  it  under  a  pressure  of,  from  20  Ibs. 

M  2 


164 


IRON  AND   STEEL. 


to  25  Ibs.  per  square  inch  to  enter  the  vessel  through  the 
twyer  holes. 

The  Ladles. — These  vessels,  which  are  used  for  bringing 
the  molten  pig  iron  to  the  converter  and  for  receiving  the 
finished  product,  must  correspond  in  dimensions  to  the 

converters  with  which 
they  are  used,  as  they 
have  to  hold  the  full 
charge  of  metal  in  each 
case.  The  feeding 
ladle,  which  consists  of 
an  iron  shell  lined  with 
EIG.  31.— Tilting  Ladle.  a  course  of  firebricks, 

is  mounted  on  a  trolley, 

and  is  fitted  with  hand-gearing  so  arranged  that  the  ladle 
moves  laterally  towards  the  converter  at  the  same  time  as 
it  is  tilted  over  the  mouth.  So  that  when  the  metal  is  ready 
to  run  the  lip  is  well  over  the  mouth  of  the  converter,  which 
has  been  brought  into  the  horizontal  position  for  receiving 
the  charge.  The  actual  tilting  is  often  done  by  attaching 
a  chain  to  the  off- side 
of  the  ladle,  and  raising 
it  by  means  of  an  over- 
head travelling  crane. 
The  general  form  of 
the  ladle  is  shown  in 
Fig.  31.  It  is  drawn 
along  the  platform  in 
front  of  the  converter 

by  a  steel  rope.  The  casting  ladle  (Fig.  32),  which  receives 
the  finished  metal,  consists  of  a  wrought  iron  shell  with  a 
ganister  lining  that  slopes  from  all  parts  to  the  tap  hole  in 
the  bottom.  This  is  closed  by  a  clay  stopper  attached  to 
an  iron  rod  coated  with  fireclay  where  it  is  likely  to  come 
into  contact  with  the  molten  metal.  The  upper  part  of  the 


FIG.  32. — Casting  Ladle. 


THE   BESSEMER  PROCESS.  165 

rod  is  bent  over  the  side  in  the  form  of  a  swan's  neck,  so  as  to 
pass  through  guides  fixed  to  the  outside  of  the  ladle.  It  is 
also  connected  with  the  short  arm  of  a  lever  in  such  a  way 
that  when  the  long  arm  is  raised  the  plug  is  lifted  out  of 
the  tap  hole,  and  when  it  is  lowered  the  plug  is  pushed 
back  again.  This  ladle  is  suspended  on  trunnions  from  the 
horizontal  arm  of  a  hydraulic  crane  having  a  circular 
motion  ;  it  can  thus  be  brought  under  the  mouth  of  the 
converter  to  receive  the  charge,  and  then  over  the  moulds 
in  the  casting  pit  to  cast  the  metal. 

The  converters,  when  there  are  several  of  them,  are 
arranged  in  a  row,  with  a  platform  running  along  in  front 
of  them  at  such  a  height  that  when  the  converters  are 
horizontal  their  mouths  are  just  above  it.  The  charging 
is  carried  out  on  this  platform. 

Working  the  Charge. — The  converter  is  hot  from  a  previous 
blow,  or,  if  newly  lined,  has  been  heated  by  blowing  coke  in 
it.  The  ladle  containing  the  full  charge  of  molten  metal  is 
raised  to  the  platform  by  a  hydraulic  lift,  and  drawn  in 
front  of  the  converter.  The  metal  is  then  run  in,  the  blast 
turned  on,  and  the  converter  brought  into  the  vertical 
position.  The  pressure  of  the  blast  and  the  narrowness  of 
the  twyer  channels  through  which  it  is  driven  prevents  the 
metal  from  running  back  into  the  blast  box,  and  the  re- 
actions proceed  rapidly.  The  silicon  burns  to  form  silica, 
which  unites  with  basic  oxides  to  form  a  slag,  and  there  is 
very  little  flame  during  this  part  of  the  blow,  as  no  com- 
bustible gases  are  formed.  Then  the  carbon  burns  with 
formation  of  carbon  monoxide,  which  gives  a  brilliant  flame 
at  the  converter  mouth.  Particles  of  iron  and  slag  are  also 
driven  out,  causing  a  shower  of  sparks.  When  the  carbon 
is  all  burnt  the  flame  drops,  and  if  the  blowing  is  con- 
tinued the  metal  itself  will  oxidise  rapidly.  The  dropping 
of  the  flame  is  usually  taken  as  the  indication  that  this 
part  of  the  operation,  which  lasts  from  ten  to  fifteen  minutes, 


166  IEON  AND   STEEL. 

is  finished.  The  converter  is  then  turned  down,  and  the 
blast  cut  off.  The  bath  is  now  ready  for  the  spiegeleiseii  or 
the  ferro-inanganese  to  be  added.  If  the  addition  is  only  a 
small  proportion  of  the  whole  charge  it  may  be  thrown  into 
the  converter  cold,  but  if  a  larger  proportion  is  to  be  added 
it  must  be  heated  before  it  is  thrown  in.  The  metal  is  then 
ready  to  be  run  into  the  casting  ladle,  which  is  brought 
under  the  mouth,  and  receives  the  full  charge.  The  molten 
metal  in  the  ladle  is  covered  with  a  layer  of  slag  that  has 
run  from  the  converter  with  it.  This  protects  the  metal 
from  the  air,  and  prevents  the  too  rapid  escape  of  heat 
from  it.  The  ladle  is  then  brought  over  the  casting  pit, 
the  tap-hole  opened,  and  the  metal  run  into  the  ingot 
moulds  placed  there  to  receive  it.  The  moulds  are  heavy  iron 
castings,  having  a  rectangular  cross-section  with  the  corners 
rounded  off.  They  are  open  at  the  bottom,  and  a  little  wider 
there  than  at  the  top,  so  that  they  may  be  readily  stripped 
from  the  ingots.  For  casting  they  are  placed  vertically  on 
an  iron  plate  in  the  bottom  of  the  casting  pit,  and  when  the 
metal  has  set  sufficiently  for  handling  they  are  lifted  off  by 
a  crane,  and  the  ingots  removed  in  a  similar  manner.  The 
further  treatment  of  these  ingots  will  be  described  later. 

Analyses  of  the  gas  taken  from  the  converter  at  intervals 
during  the  blow  show  that  some  of  the  carbon  is  burnt  at 
the  same  time  as  the  silicon,  but  as  the  temperature  is 
lower  it  is  burnt  to  carbon  dioxide  and  escapes  as  such. 
Later,  when  the  greater  part  of  the  silicon  has  burnt,  and 
the  main  bulk  of  the  carbon  is  burning,  the  temperature  is 
higher  and  carbon  monoxide  is  the  gaseous  product.  Thus 
the  carbon  dioxide  was  found  to  decrease  from  10'7  per  cent, 
to  1*3  per  cent.,  and  the  carbon  monoxide  to  increase  from 
0  to  31  per  cent,  in  the  course  of  a  blow.  The  nitrogen 
decreases  from  88*4  per  cent,  to  66  per  cent.  The  high 
percentage  of  nitrogen  during  the  earlier  part  of  the  blow 
shows  conclusively  that  the  oxygen  of  the  blast  is  being 


THE  BESSEMER  PROCESS.  167 

principally  absorbed  by  the  silicon  in  the  charge.  In  the 
early  days  of  the  process  the  character  of  the  flame  was 
carefully  noted,  and  the  flame  itself  was  looked  at  through  a 
spectroscope  to  observe  the  appearance  and  disappearance 
of  certain  lines  in  its  spectrum.  Now  the  experience  of 
the  blower  is  more  depended  upon,  and  the  spectroscope 
but  little  used.  The  manganese  present  in  the  pig  is 
oxidised  and  passes  into  the  slag,  but  the  phosphorus  is 
practically  unchanged.  Oxide  of  iron  is  formed  freely,  and 
is  in  part  removed  in  the  slag ;  the  remainder  is  left  in  the 
molten  metal  to  be  reduced  by  the  deoxidiser. 

If  too  little  silicon  is  present  the  blow  is  "  cold  "  ;  that 
is,  the  temperature  does  not  rise  sufficiently  for  a  good 
finish.  According  to  Howe  about  1*25  per  cent,  silicon  is 
the  best  for  general  blowing;  but  in  American  practice 
metal  with  as  low  as  0*66  per  cent,  silicon  is  blown,  and 
the  difficulty  is  got  over  by  using  a  converter  with  a  larger 
bottom  and  twyer  area,  so  that  the  bath  of  metal  is  not  so 
deep,  and  the  blowing  more  rapid.  The  duration  of  such  a 
blow  is  usually  less  than  ten  minutes,  and  the  blows  are 
made  to  follow  each  other  rapidly.  In  this  way  the 
converter  is  kept  very  hot,  and  the  finished  metal  is  good 
in  spite  of  the  low  silicon  content  of  the  pig.  This  rapid 
working  has  been  tried  at  Barrow,  but  was  not  found 
suitable  for  the  grade  of  pig  iron  produced  there,  nor  for 
the  atmospheric  and  other  conditions  obtaining  in  this 
country.  The  twyer  blocks  in  the  Barrow  converters  were 
reduced  from  33  to  24  twyers,  for  the  metal  was  found  to 
be  so  hot  at  the  end  of  the  blow  as  to  be  quite  unmanageable. 
In  Sweden  low  silicon  irons  are  blown,  but  the  metal  is 
very  hot  at  the  beginning. 

On  the  other  hand,  if  the  silicon  content  is  too  high  the 
temperature  rises  too  much,  and  this  does  not  give  satis- 
factory results.  But  this  difficulty  can  be  overcome  by  the 
addition  of  cold  scrap  ;  this  is  known  as  "  scrapping."  But 


168 


IRON  AND   STEEL. 


this  can  be  avoided  by  the  use  of  a  mixer  from  which 
molten  metal  of  fairly  uniform  composition  can  be  taken. 
According  to  Siemens  the  oxidation  of  silicon  in  the  molten 


FIG.  33. — Converter  and  Cranes  in  Bessemer  Shop. 

A,  Converter.  c,  Casting  crane.  E,  Ingot  mould. 

B,  Tilting  ladle.  D,  Casting  ladle.  F,  Ingot  crane. 

bath  determines  the  oxidation  of  iron  to  furnish  the  silica 
formed  with  a  basic  oxide.  The  general  arrangement  of  the 
converter  and  cranes  in  a  Bessemer  shop  is  shown  in  Fig.  33. 
The  composition  of  Bessemer  pig  used  in  different  countries 
and  in  different  parts  of  the  same  country  varies  consider- 
ably ;  but  the  following  table  will  give  an  idea  of  the 
working  limits  :— 


Carbon. 

Silicon. 

Manganese. 

Phosphorus. 

Sulphur. 

Limits  of 

composi- 

tion 

4-4  to  3-1 

2-5  to  0-6 

3  to  0-1 

0-4  to  0  02 

0-1  5  to  0-02 

Typical 

Pig 

3-5 

2 

0-3 

0-05               O-Oo 

Finished 

Variable  but 

metal     . 

fairly  under 

0-04 

(HI 

0-06               0-05 

control. 

THE  BESSEMER   PEOCESS.  169 

The  slags  formed  are  very  acid  in  character  and  not  at  all 
uniform  in  composition,  some  portions  not  having  properly 
fused.  The  fluid  portion  runs  from  the  converter,  and 
collects  upon  the  top  of  the  metal  in  the  ladle  as  already 
described;  the  remainder  is  tipped  out  by  inverting  the 
converter  after  the  metal  has  been  run.  An  average  com- 
position of  slag  taken  from  the  converter  at  different  periods 
of  the  blow  is  given  below  : — 

Composition  of  Acid  Bessemer  Slag. 

Silica,  Si02 55'0 

Manganese  oxide,  MnO        .         .         .         .  27 '0 

Ferrous  oxide,  FeO IB'O 

Alumina,  AlaOs    ......  3'0 

Lime,  CaO 1'5 

Magnesia,  MgO  ......  0'5 


lOO'O 

There  are  three  ways  in  which  the  molten  pig  may  be 
prepared  for  the  process. 

(1)  It  may  be  run  directly  from  the  blast  furnace  into 
the  feeding  ladle,  and  is  then  known  as  "direct  metal." 
But    this    means    that   the    smelting    furnace    must    be 
sufficiently  near  to  the  Bessemer  plant  for  the  metal  to  be 
brought  to   it  without   undue    cooling,  and  that   a  fairly 
regular  supply  can  be  guaranteed,  or  the  working  of  the 
plant  will  be  intermittent,  and  therefore  costly. 

(2)  The  metal  in  the  form  of  pigs  may  be  melted  down 
in  a  cupola  and  run  into  a  ladle  for  transference  to  the 
converter.      This    was    the   method    usually   adopted,    as 
regular  working  of  the  plant  could  then  be  ensured.     The 
cupolas  used  for  this  purpose  vary  from  8  feet  to  10  feet  in 
outside  diameter,  and  are  14  feet  to  24  feet  high  up  to  the 
charging  door.     They  are  worked  with  a  blast  pressure  of 


170  IEON  AND   STEEL. 

J  Ib.  to  J  Ib.  per  square  inch.  The  largest  will  melt  about 
16  tons  of  pig  per  hour  with  the  consumption  of  1  ton  of 
coke.  Some  of  the  silicon  is  oxidised  and  removed,  which 
is  an  advantage  with  high  silicon  pig,  but  the  reverse  when 
the  silicon  is  low.  It  allows,  however,  of  the  charge  being 
mixed  to  suit  the  requirements.  This  method  is  being 
largely  used,  but  will  probably  gradually  disappear. 

(3)  The  most  recent  method  is  to  take  the  molten  metal 
from  a  mixer,  which  is  a  kind  of  reservoir  for  the  molten 
metal  from  the  blast  furnace.  This  method,  which  will 
be  described  in  the  next  chapter,  allows  of  very  uniform 
working. 

The  loss  of  metal  from  pig  to  steel  varies  somewhat,  but 
does  not  exceed  9  to  12  per  cent,  for  direct  metal,  and  14 
to  15  per  cent,  for  cupola  metal. 

The  Basic  Bessemer  Process. — It  has  been  known  for  a 
long  time  that  when  the  amount  of  silica  in  a  refining  slag 
exceeds  30  per  cent,  that  phosphorus  will  not  pass  into  it, 
and  that  practically  the  whole  of  that  element  present  in 
the  pig  iron  is  found  in  the  refined  metal.  For  this  reason 
pig  iron  containing  a  notable  quantity  of  phosphorus  cannot 
be  treated  in  a  silica-lined  converter,  as  the  slag  formed  is 
very  acid  in  character.  It  was  also  known  that  a  sufficiently 
basic  slag  would  take  up  practically  the  whole  of  the 
phosphorus  from  a  very  phosphoric  pig,  with  the  production 
of  good  workable  metal.  But  it  was  also  thought,  although 
erroneously,  that  at  a  very  high  temperature  phosphorus 
would  not  pass  even  into  a  basic  slag.  This  tended  to 
retard  progress. 

As  early  as  1872  Mr.  Snelus  succeeded  in  reducing  the 
phosphorus  in  a  charge  of  molten  pig  from  2  per  cent, 
down  to  Ol  per  cent,  by  the  use  of  a  basic  lining,  but  not 
in  a  Bessemer  converter,  and  Mr.  E.'Riley  had  worked  in 
the  same  direction.  It  was  left,  however,  to  Messrs. 
Thomas  and  Gilchrist  to  perfect  a  practical  method  for 


THE  BESSEMEE  PEOCESS. 


171 


treating  phosphoric  pig  iron  by  the  Bessemer  process,  and 
in  doing  this  they  received  the  assistance   of   such  well 


FIG.  34. — Bessemer  Converter  in  Position. 

known  men  as  E.  P.  Martin,  Windsor  Eichards,  and  J.  E. 
Stead. 

The  chief  difficulty  lay  in  the  selection   of   a  suitable 
lining,  but    dolomite   lime    was   finally   selected,   and    the 


172  IEON  AND   STEEL. 

difficulties  attending  its  use  on  the  large  scale  overcome. 
The  process  was  first  carried  to  a  commercial  success 
in  the  works  of  Messrs.  Bolckow,  Vaughaii  &  Co.  at 
Middlesborough. 

The  Basic  Lining. — The  substitution  of  a  basic  for  an 
acid  lining  constitutes  the  essential  difference  between  the 
two  processes  ;  and  dolomite  lime  appears  to  be  the  only 
generally  suitable  material,  although  lime  itself  has  been 
successfully  used.  The  principal  difficulties  are  due  to  the 
great  shrinkage  which  dolomite  undergoes  when  it  is  burnt 
to  form  the  lime,  and  to  the  fact  that  water  cannot  be  used 
in  the  moulding  process.  The  dolomite  is  first  burnt  at  a 
temperature  sufficiently  high  to  effect  the  maximum  shrink- 
age, but  not  high  enough  to  cause  the  pieces  of  stone  to 
cinter  into  a  solid  mass.  A  basic-lined  cupola  worked  with 
a  blast  pressure  of  1  Ib.  per  square  inch,  and  burning  1^  cwt. 
of  coke  per  ton  of  raw  stone,  gives  the  best  results.  The 
coke  and  stone  are  charged  in  alternate  layers  at  the  top, 
and  the  burnt  stone  is  raked  out  through  a  door  in  the 
bottom.  The  partially  burnt  pieces  are  picked  out  and 
returned  to  the  cupola,  none  but  properly  burnt  stone  being 
passed  on.  This  is  then  ground  to  a  coarse  powder  in  a 
mill  under  edge  runners,  and  then  mixed  with  hot,  well- 
boiled  tar  to  render  the  mass  plastic.  It  may  then  be  used 
for  ramming  round  a  core  to  form  the  converter  lining,  as 
already  described  for  the  acid  process ;  or,  as  is  more 
common,  it  is  moulded  into  bricks  by  being  subjected  to 
considerable  pressure  in  a  powerful  hydraulic  press.  The 
moulds  in  which  the  bricks  are  made  are  shaped  so  that 
the  bricks  will  follow  the  curve  of  the  converter  shell,  and 
can  be  set  without  the  use  of  mortar  of  any  kind.  In 
lining  the  converter,  the  bricks  are  built  a  little  away  from 
the  shell,  and  the  space  between  is  rammed  in  with  the 
same  mixture  as  is  used  for  making  the  bricks.  This  tends 
to  drive  the  bricks  inwards,  and  force  them  closer  together. 


THE   BESSEMER   PROCESS.  173 

Formerly  the  bricks  were  burnt  at  a  low,  red  heat  after 
moulding;  but  now  they  are  brought  straight  from  the 
press,  with  the  exception  of  a  few  burnt  ones  to  form  the 
bottom  rows.  Fig.  34  shows  the  concentric  form  of  con- 
verter, which  is  almost  entirely  used  in  the  basic  process. 

The  Basic  Bottom. — This  is  formed  differently  from  the 
acid  bottom.  There  is  the  usual  frame  and  bottom  plate, 
which  also  forms  the  top  of  the  blast  box,  in  which  are  a 


FIG.  35. — Converter  Bottom  in  Eepairing  Shop. 

number  of  holes  corresponding  to  the  number  of  air 
channels  required  in  the  twyer  plug,  or  central  portion  of 
the  bottom.  Iron  rods  are  placed  upright  in  these  holes,  a 
large  iron  ring  fixed  round  them,  and  the  dolomite  mixture 
well  rammed  in  between  the  rods  with  a  circular  rammer 
having  a  central  hole  large  enough  for  a  rod  to  pass  through. 
In  this  way  they  are  uniformly  rammed  round.  The  iron 
ring  is  then  withdrawn,  and  the  remainder  of  the  bottom 
rammed  in.  When  the  rods  are  taken  out,  channels  are 


174  IRON  AND   STEEL. 

left  for  the  passage  of  the  blast  from  the  chest  to  the  interior 
of  the  converter.  The  bottom  is  brought  into  position  and 
secured  as  already  described.  Fig.  35  shows  a  bottom  in 
the  repairing  shop.  The  grinding  mills  for  the  basic  material 
are  on  the  right. 

The  Process. — The  details  of  a  blow  vary  somewhat  in 
different  works,  so  that  the  following  must  be  taken  as  a 
general  description.  The  converter  is  already  hot  from  a 
previous  charge,  or  has  been  heated  by  blowing  fuel  in  it. 
A  quantity  of  lime,  about  3  cwt.  per  ton  of  metal,  is  added, 
together  with  some  coal,  and  blown  until  hot.  The  con- 
verter is  then  brought  down,  and  the  charge  of  molten  pig 
run  in  from  the  tilting  ladle.  The  blast  is  now  turned  on, 
the  converter  rotated  into  the  vertical  position,  and  the 
blowing  continued.  In  about  10  minutes  the  silicon,  the 
carbon,  and  the  greater  part  of  the  manganese,  together 
with  a  small  part  of  the  phosphorus,  have  been  oxidised, 
and  the  flame  drops  ;  the  blow  is  continued  for  2  or  3 
minutes,  during  which  the  remainder  of  the  phosphorus  is 
oxidised.  There  is  no  positive  indication  of  the  disappear- 
ance of  the  whole  of  the  phosphorus  from  the  metal ;  but 
long  and  careful  observation  enables  the  blower  to  detect 
even  slight  changes  in  the  appearance  of  the  flame.  He  is, 
therefore,  able  to  tell  how  the  blowing  is  proceeding,  and 
when  the  metal  is  ready  for  the  deoxidiser.  However,  he 
is  unable  to  rely  entirely  on  his  judgment,  so  that  the  con- 
verter must  be  brought  down  at  intervals  during  this  after- 
blow,  a  sample  dipped  out  with  a  small  ladle,  and  tested. 
For  this  purpose  the  metal  is  poured  into  a  round  mould, 
hammered  into  a  round  plate  about  J  inch  thick  under  a 
small  steam  hammer,  broken  across,  and  the  fracture 
examined.  An  expert  can  tell  from  the  appearance  of  the 
fracture  whether  the  blow  is  to  be  resumed,  or  whether  it 
has  gone  far  enough.  The  presence  of  phosphorus  causes 
the  metal  to  crystallise,  and  as  the  element  disappears  the 


THE   BESSEMER   PROCESS.  17o 

size  of  the  crystals  decreases.     The  blowing  is  continued 
until  the  test  piece  shows  a  granular  fracture. 

When  the  blow  is  finished,  the  slag  is  run  into  a  truck 
on  the  roadway  below  the  platform,  or  on  the  floor  directly 
under  the  converter,  and  the  bath  of  metal  is  ready  for  the 
addition  of  the  deoxidiser.  If  mild  steel  is  being  made, 
the  weighed  quantity  of  ferro-manganese,  broken  up  into 
small  lumps  and  made  red  hot,  is  shovelled  into  the  con- 


FIG.  36. — Casting  Basic  Steel  at  Spring  Vale  Works. 

verier,  and  the  bath  allowed  to  stand  for  a  few  minutes  to 
soak.  It  is  then  run  into  the  casting  ladle  and  taken  to 
the  casting  pit.  The  ladle  in  position  over  the  moulds  is 
shown  in  Fig.  36.  While  the  bath  is  standing,  after  the 
addition  of  the  ferro  manganese,  reactions  are  set  up  by 
which  some  phosphorus  is  caused  to  pass  back  into  the 
metal,  but  the  blower  always  blows  the  metal  until  the 
percentage  of  phosphorus  is  lower  than  that  allowed  in  the 
finished  metal,  so  as  to  compensate  for  this  passing  back. 


176  IEON   AND   STEEL. 

Sometimes  the  converter  is  turned  up,  after  the  addition  of  the 
ferro-manganese,  and  the  blow  continued  for  a  few  seconds 
before  the  metal  is  poured.  The  casting  ladle  in  position 
over  a  mould  is  also  shown  in  Fig.  33.  If  higher  carbon 
metal  is  required,  as  for  the  production  of  rail  steel  with 
about  0*4  per  cent,  of  carbon,  the  addition  is  not  made  to 
the  converter.  The  metal  is  run  into  the  ladle  with  as 
little  slag  as  possible,  and  the  proper  proportion  of  molten 
spiegeleisen  added  to  it  there.  But  the  changes  indicated 
above  still  take  place,  for  it  is  impossible  to  prevent  some 
slag  from  running  into  the  ladle  and  forming  a  layer  on  the 
top  of  the  metal.  The  carbon  and  manganese  of  the 
spiegeleisen  react  on  this  slag,  and  a  little  phosphorus  is 
reduced  and  passes  back  into  the  metal. 

The  oxidation  of  the  phosphorus  during  the  after-blow 
seems  to  determine  the  oxidation  of  iron  to  a  greater 
extent  than  in  the  acid  process,  and  the  addition  of  2  to  3 
per  cent,  of  manganese  is  necessary  to  obtain  metal  workable 
at  a  red  heat,  for  the  oxygen  must  be  cleared  out  while 
some  manganese  is  still  left  in  the  metal.  It  would  appear, 
according  to  some  authorities,  that  if  carbon  monoxide  is 
formed,  it  acts  upon  the  phosphate  in  the  slag,  and 
phosphorus  passes  back  into  the  steel ;  but  manganese 
acts  as  a  cover  for  the  carbon  by  preventing  its  rapid  oxida- 
tion, so  that  as  long  as  manganese  is  present,  phosphorus 
remains  in  the  slag.  Stead,  however,  is  of  opinion  that 
manganese  itself  will  reduce  phosphate  of  lime,  and  he  thus 
accounts  for  the  phosphorus  that  passes  back  into  the 
metal. 

If  a  manganiferous  pig  is  being  blown,  it  is  found  that 
as  much  as  0'2  to  0*3  per  cent,  of  manganese  may  be  left 
in  the  metal  after  the  phosphorus  has  been  removed,  and 
as  this  tends  to  prevent  over-oxidation  during  the  after- 
blow,  less  ferro-manganese  or  spiegeleisen  is  required  to  be 
added.  Also  other  additions,  such  as  haematite  pig,  silicon- 


THE  BESSEMER  PEOCESS.  177 

spiegel,  and  carbonaceous  matters  have  been  used  in  order 
to  reduce  the  quantities  of  the  usual  deoxidisers  to  be 
added.  In  the  case  of  the  higher  carbon  steels,  it  should 
be  noticed  that  the  deoxidiser  is  also  the  recarburiser. 

The  removal  of  sulphur  does  not  appear  to  be  by  any 
means  certain.  Sometimes  it  is  nearly  all  eliminated,  at 
others  a  considerable  proportion  remains  in  the  finished 
metal.  To  obtain  sulphur-free  metal  a  manganiferous  pig, 
in  which  the  sulphur  is  always  low,  should  be  used. 

The  slag  is  an  important  item  in  the  basic  process,  for  it 
contains  much  phosphate  of  lime,  and  is  valuable  as  a 
manure.  It  is  removed  from  the  Bessemer  shop  to  the  slag 
mill,  broken  up  and  ground  to  a  fine  powder.  It  is  then 
ready  for  the  market.  The  composition  of  the  slag  must 
be  controlled  as  far  as  possible,  and  frequent  analyses  of  it 
made,  for  the  presence  of  much  oxide  of  iron  in  it  means 
loss  of  metal  from  the  charge,  and  a  correspondingly  lower 
output.  Sufficient  lime  must  be  added  to  prevent  this. 
The  lime  should  be  of  good  quality,  with  a  low  content  of 
silica,  as  this  acid  oxide  requires  from  three  to  four  times 
its  weight  of  lime  to  slag  it  off,  with  a  consequent  decrease 
in  the  lime  available  for  the  removal  of  phosphorus.  The 
following  will  give  a  general  idea  of  the  composition  of 
basic  slag : — 

Lime,  CaO 50'0 

Phosphoric  oxide,  P205       .         -         .  20*0 

Ferrous  oxide,  FeO     .  15*5 

Silica,  Si02          .  7'0 

Manganous  oxide,  MnO 

Alumina,  A1203 

Magnesia,  MgO 

Sulphur,  S  0-5 


i.s. 


100-0 

N 


178 


IKON  AND  STEEL. 


The  general  composition  of  the  pig  iron  used,  and  of  the 
finished  product,  is  shown  below  : — 


Carbon. 

Silicon. 

Manganese. 

Phosphorus. 

Sulphur. 

General 

limits     . 

3-3  to  3-6 

0-54  to  1'7 

0-4  to  1-5 

1-2  to  3-0 

0-03  to  0-1  5 

Suitable 

P*g 

F  i  nished 

3-2 

Variable  but 

1-5 

0-5 

2"2 

0-06 

steel 

fairly  under 

control. 

0-016 

0-54 

0-092 

0-04 

It  is  just  as  necessary  that  the  phosphorus  content  of 
"  basic  "  pig  should  not  fall  below  a  certain  limit  as  that 
there  should  be  sufficient  silicon  in  "  acid "  pig.  The 
reason  for  this  is  that  the  character  of  the  blow  depends 
upon  the  amount  of  phosphorus  to  be  oxidised,  and  if  there 
is  not  sufficient,  a  cold  blow  is  the  result,  that  is,  the  metal 
is  too  cold  for  satisfactory  casting,  and  skulls,  or  masses  of 
solidified  metal,  are  left  in  the  ladle.  On  the  other  hand 
the  silicon  content  must  not  be  too  high  or  the  blow  is 
hotter  than  it  should  be,  and  equally  unsatisfactory  results 
are  obtained.  Sometimes  a  very  siliceous  basic  pig  has  its 
silicon  blown  down  in  an  acid  lined  converter,  and  is 
finished  in  a  basic  lined  one.  The  judicious  addition  of 
cold  steel  scrap  is  very  useful  in  the  case  of  very  hot  blows, 
and  is  known  as  "  scrapping."  Fig.  37  shows  the  cranes 
and  moulds  in  position,  and  gives  an  idea  of  the  cramped 
condition  of  a  Bessemer  shop. 

Small  Converters. — Such  vessels  are  still  in  use  where 
small  charges  of  steel  are  manufactured,  and  are  either 
fixed  or  arranged  for  tipping,  as  the  case  may  be.  They 
are  side  blown,  and  with  the  fixed  converters  the  finished 
metal  is  tapped  from  a  tap-hole  which  is  plugged  with  clay 


THE  BESSEMEE  PEOCESS. 


179 


while  the  blow  is  going  on.  The  blast  box  is  usually  in 
the  form  of  a  belt  round  the  body  of  the  converter,  and  the 
twyers  lead  from  it  through  the  side  lining.  The  blast 
pressure  is  lower  than  is  used  for  bottom  blown  vessels,  and 
averages  about  6  Ibs.  per  square  inch.  High  quality  metal 
is  produced  in  Sweden  in  acid  lined  converters  of  this  type, 
but  it  is  only  fair  to  say  that  the  pig  iron  used  is  of 


FIG.  37. — Moulds  and  Cranes  in  Bessemer  Shop. 

exceptional  quality.  The  carbon  in  the  finished  metal  may 
be  high  enough  for  high  grade  tool  steel,  as  the  following 
analysis  will  show  : — 

Carbon  =  1*3  ;  Manganese  —  0'4  ;  Silicon  =  0'05  ;  Phos- 
phorus =  0*02  ;  Sulphur  =  Trace. 

In  this  country  the  Hatton  modification  of  the  Clapp- 
Griffiths  fixed  converter  is  one  of  the  best  forms.  The 
original  converter  had  a  fixed  bottom,  but  Mr.  Hatton  made 

N  2 


180  IRON  AND  STEEL. 

the  bottom  movable,  which  offers  greater  facilities  for 
working  and  repairs.  The  vessel  is  side  blown,  and  the 
twyers,  which  are  round  the  circumference  and  a  few  inches 
above  the  bottom,  are  connected  with  the  blast  belt  by  a 
descending  pipe  that  can  be  easily  moved  aside  when  a 
twyer  is  to  be  replaced.  High  grade  pig  containing  about 
2  per  cent,  of  silicon  is  used,  and  a  blow  requires  about 
15  minutes  from  the  time  the  molten  metal  is  run  in.  The 
oxidation  of  iron  is  excessive,  and  the  loss  of  metal  is  about 
20  per  cent,  of  the  charge.  Only  dead  soft  metal  can  be 
produced  ;  but  it  is  of  excellent  quality,  the  carbon  being 
about  O'l  per  cent.,  and  the  phosphorus  and  sulphur  low. 

The  Robert  Converter  is  an  example  of  a  small  side-blown 
tipping  vessel  of  the  eccentric  type.  It  is  circular  in 
horizontal  section  with  a  fiat  side,  so  that  it  takes  somewhat 
the  form  of  a  D.  The  twyers  pass  through  the  flat  side, 
and  are  inclined  a  little  towards  each  other  as  they  pass 
through  the  lining,  so  as  to  blow  more  towards  the  centre 
of  the  bath.  It  is  claimed,  however,  that  the  blast  does 
not  penetrate  the  metal  very  far,  but  refines  it  by  a  kind  of 
surface  action.  The  inclination  of  the  twyers  can  be 
altered  by  tipping  the  converter  into  various  positions.  A 
large  excess  of  air  is  used,  so  that  the  carbon  is  probably 
burnt  straight  to  carbon  dioxide,  and  the  temperature  of 
the  bath  thus  increased.  The  converter  may  be  either 
acid  or  basic  lined  to  suit  non-phosphoric  or  phosphoric  pig 
as  the  case  may  be.  Ferro-manganese,  and  sometimes 
ferro-silicon,  is  added  at  the  end  of  the  blow,  and  the 
finished  metal  is  run  from  the  neck  by  tilting  the  vessel. 
Such  converters  are  more  suitable  for  the  production  of 
steel  castings  than  for  ingot  metal. 

The  principal  difficulty  in  dealing  with  these  small 
charges  is  to  keep  the  metal  sufficiently  fluid  to  cast  well, 
and  this  is  overcome  in  the  Walrand-Legenissel  process  by 
running  in  a  calculated  quantity  of  ferro-silicon  after  the 


THE  BESSEMER  PEOOESS. 


181 


carbon  has  been  blown  out,  and  then  turning  up  the 
converter  again  for  an  after-blow,  during  which  the  silicon 
is  rapidly  burnt  and  the  temperature  of  the  bath  increased. 
The  ferro-manganese  is  then  added,  and  the  metal  is  ready 
to  pour.  Small  bottom-blown  converters  that  can  be 
rotated  by  hand  gearing,  and  taking  charges  of  6  cwts.  to 
12  cwts.,  are  used  in  the  process,  and  sound  steel  castings 
of  excellent  quality  are  obtained. 

The  uses  to  which  Bessemer  steel  is  put  depend  largely 
upon  the  amount  of  carbon  present.  A  general  idea  is 
given  by  the  following  table  :— - 

...  0-25  per  cent.  C. 

...  0-30 

...  o'40 

...  0-50 


Ship  plates 

...     0-2 

per  cent.  0. 

Axles  .  .  . 

Boiler  ... 

...     0-2 

}  , 

Tyres  ... 

Shafting 

...     0-2 

.  ? 

Rails  ... 

Sheets  ... 

...     0-2 

M 

Springs 

CHAPTEK   VIII. 

THE    OPEN    HEARTH    PROCESS. 

THE  very  high  temperature  generated  in  the  Bessemer 
acid  or  basic  converter  by  the  rapid  burning  of  the  silicon, 
carbon,  and  phosphorus  is  sufficient  to  keep  even  low 
carbon  metal  in  a  condition  for  satisfactory  casting  ;  and 
this,  together  with  the  rapid  output,  made  it  difficult  to 
devise  an  ordinary  furnace  method  that  should  prove  a 
serious  rival  to  the  Bessemer  process.  Sir  William 
Siemens  and  his  brother,  however,  overcame  all  difficulties 
at  the  cost  of  much  labour  and  capital,  and  gave  to  the 
iron  world  a  method  of  steel  making  that  is  more  under 
control  than  the  Bessemer  process,  and  by  which  large 
quantities  of  iron  and  steel  are  made  in  all  iron-producing 
countries. 

It  is  an  open  hearth  or  reverberatory  furnace  method, 
and  although  the  furnace  itself  has  undergone  considerable 
modification  as  regards  detail,  it  is  the  same  in  principle 
and  general  working  as  when  first  introduced.  Clearly  the 
principal  factor  to  the  general  success  of  such  a  method  is 
the  generation  of  a  sufficient  temperature  to  obtain  a  large 
mass  of  low  carbon  metal  in  a  condition  for  tapping  into  a 
ladle,  and  casting  into  ingots,  after  the  refining  and  finishing 
operations  have  been  carried  out.  This  is  effected  in  the 
open  hearth  by  the  use  of  the  principle  of  regeneration, 
which  was  first  made  a  practical  success  by  Siemens  ;  and 
the  adaptation  of  this  principle  to  the  reverberatory  furnace 
is  the  leading  feature  of  the  Siemens'  and  all  the  more 
modern  open  hearths. 


THE   OPEN  HEARTH  PEOCESS. 


183 


The  Regenerative  Furnace. — A  description  of  the  puddling 
furnace  has  already  been  given,  so  that  the  type  of  furnace 
is  familiar.  The  hearth  of  the  furnace  in  which  the 
puddling  process  is  carried  on  is  heated  by  the  passage  of 
the  products  of  combustion  of  solid  fuel  from  the  grate  on 
their  way  to  the  flue,  and  the  heat  is  concentrated  on  the 
hearth  by  the  lowness  of  the  roof  above  it.  Such  a  furnace 
works  in  one  direction  only ;  but  it  is  easy  to  imagine  a 


FIG.  38. — Regenerative  Open  Hearth  (longitudinal  section). 

A,  Working  bed  or  hearth.  D,  Air  regenerator. 

B,  Working  doors.  E,  Air  port. 

C,  Gas  regenerator.  F,  Gas  port. 

fire-grate  and  chimney  at  each  end  of  the  bed,  so  that  the 
furnace  could  be  fired  from  both  ends  alternately.  This  is, 
in  effect,  the  principle  of  the  regenerative  furnace,  but  the 
firing  is  carried  on  by  burning  hot  producer  gas  in  hot  air, 
the  heating  of  the  gas  and  air  being  effected  by  utilising 
the  waste  heat  of  the  furnace  itself.  The  application  of  the 
principle  of  regeneration  requires  that  the  combustion 
should  be  carried  on  at  both  ends  of  the  hearth  alternately. 
As  the  burning  of  hot  producer  gas  in  hot  air  gives  a  much 


184  IRON  AND   STEEL. 

higher  temperature  than  could  be  obtained  by  burning 
solid  fuel,  or  by  burning  cold  gas  in  ordinary  air,  the  heat 
of  the  furnace  is  sufficient  to  raise  mild  steel  well  above 
the  casting  temperature,  so  that  it  can  be  tapped  from  the 
furnace,  and  cast  into  ingots  without  difficulty. 

The  furnace  itself  consists  of  an  outer  casing  of  iron 
plates  riveted  together,  and  held  in  position  by  strong 
bands  fastened  by  tie  rods.  The  interior  is  lined  with  very 
refractory  material  to  resist  the  excessive  heat  obtained. 
The  roof,  sides,  and  ports  are  built  of  silica  bricks  of  the 
finest  quality,  made  from  a  pure  quartz  rock  mixed  with 
2  per  cent,  of  lime,  and  the  bed  is  lined  with  silica  sand. 
The  bottom  consists  of  cast-iron  or  steel  plates,  which  are 
carried  by  strong  girders  supported  on  the  foundation 
walls.  The  bottom  plates  are  faced  with  a  layer  of  silica 
bricks  w7hich  thickens  towards  the  sides  and  ends,  so  as  to 
follow  roughly  the  curved  surface  of  the  finished  bed,  and  a 
hole  about  18  inches  square  is  left  on  the  tapping  side  of 
the  furnace.  A  taper  iron  plug  is  pushed  into  this  hole 
from  outside  through  a  corresponding  hole  in  the  iron 
casing,  so  as  to  project  right  into  the  furnace.  The  plug  is 
then  well  rammed  round  with  moistened  gannister,  and 
when  this  is  well  set  the  plug  is  withdrawn  from  the  out- 
side, leaving  the  properly  formed  tap  hole.  The  tap  hole 
is  stopped  by  ramming  in  clay  from  the  outside,  and  filling 
the  remaining  part  with  anthracite  from  the  inside.  The 
temperature  of  the  furnace  is  then  raised  to  cause  small 
pieces  of  sand-stone  strewn  over  the  brick  lining  of  the  bed 
to  frit  to  the  brickwork.  The  working  lining,  consisting  of 
the  best  silica  sand,  mixed  with  a  small  proportion  of  a  more 
fusible  sand  to  cause  it  to  vitrify,  is  then  fritted  on  inch  by 
inch  until  it  attains  a  thickness  of  about  16  inches.  An 
excellent  working  surface  is  thus  obtained.  The  hearth  is 
rectangular  in  form  and  dished  out  more  or  less.  Various 
shapes  have  been  tried,  but  the  rectangular  bed  gives  the 


THE   OPEN  HEARTH  PROCESS.  185 

best  results.  The  lowest  part  of  the  bed  is  connected  with 
the  tap  hole,  which  is  at  the  back  side  of  the  furnace.  There 
are  three  working  doors  on  the  front  side,  each  of  which 
consists  of  an  iron  frame  lined  with  silica  bricks,  and 
suspended  by  a  chain  from  the  end  of  a  lever  attached  to 
the  top  of  the  furnace.  The  door  is  thus  easily  raised  or 
lowered  by  means  of  a  chain  hanging  from  the  other  end 
of  the  lever,  or  by  depressing  the  lever  itself. 

The  ends  of  the  furnace  are  exactly  similar,  and  each 
is  furnished  with  a  number  of  openings  or  ports  through 
which  the  air  and  gas  enter  the  hearth  space.  For  example, 
there  may  be  at  each  end  five  such  ports  arranged  in  two 
horizontal  rows,  three  in  the  upper  row  through  which  the 
air  enters,  and  two  in  the  lower  one  through  which  the  gas 
is  admitted.  The  brickwork  through  which  these  ports 
pass  is  usually  very  massive,  so  as  to  prevent  the  ports 
from  giving  way  under  the  excessive  heat,  and  sometimes 
hollow  castings  through  which  water  can  circulate  are 
built  in  with  the  brickwork.  The  three  air  ports  at  one 
end  communicate  by  flues  with  a  rectangular  chamber 
which  contains  a  mass  of  firebrick  forming  a  kind  of  chequer 
work.  The  arrangement  is  equivalent  to  the  three  air 
flues  opening  out  into  a  large  number  of  smaller  flues  in 
the  top  part  of  the  chamber,  and  being  gathered  together 
again  at  the  bottom  into  a  common  flue.  The  two  gas 
ports  at  the  same  end  are  connected  with  a  similar  but 
smaller  chamber,  the  flues  of  which  are  also  gathered 
together  into  a  common  flue  at  the  bottom.  The  chambers 
are  separated  by  a  thick,  well-built  dividing  wall,  so  as  to 
prevent  any  risk  of  air  and  gas  mixing  before  they  reach 
the  furnace.  The  arrangement  of  the  flues  and  chambers 
at  the  other  end  is  exactly  the  same,  for  the  two  ends  of 
the  furnace  are  duplicates  in  all  respects.  The  chambers 
are  the  regenerators,  and  are  usually  built  below  the 
furnace  level.  In  the  older  furnaces  they  formed  the 


186 


IEON  AND  STEEL. 


foundation,  and  were  put  in  first,  the  furnace  being  then 
built  on  the  top.  But  experience  has  shown  that  with 
larger  furnaces  the  weight  of  the  superstructure  is  loo 
much  for  the  walls  of  the  regenerators  to  carry.  Also,  in 
case  of  a  break  through  from  the  hearth  above,  consider- 
able damage  is  done  to  the  interiors  of  the  regenerators  by 
the  molten  metal.  The  general  practice  now  is  to  support 


FIG.  89. — Eegenerative  Open  Hearth  (transverse  section). 

A,  Tap  hole.  E,  Regenerator. 

B,  Gas  port.  F,  Casting  ladle. 

C,  Air  port.  G,  Casting  pit. 

D,  Slag  pocket. 

the  body  of  the  furnace  on  strong  girders  carried  by  separate 
piers  or  walls,  and  to  build  the  regenerators  so  as  to  leave 
the  middle  of  the  bed  quite  clear.  This  arrangement  is 
not  only  safer  and  less  troublesome  in  case  of  a  break 
through,  but  also  serves  to  keep  the  bottom  plate  cool,  as 
it  is  exposed  to  the  air  underneath. 

The  original  idea  with  regard  to  the  roof  of  the  furnace 
was  to  make  it  slope  downwards  from  both  ends  towards 
the  centre,  so  as  to  cause  the  flame  to  beat  down  on  to 


THE   OPEN  HEAETII  PEOCESS.  187 

the  bed,  but  now  tbe  roof  is  raised  a  little  in  the  centre, 
if  anything,  to  increase  the  space  above  the  hearth  so  that 
it  can  hold  a  larger  body  of  flame.  Also,  there  is  a  ten- 
dency to  build  the  ports  closer  together  and  nearer  the 
top.  A  vertical  section  of  such  a  furnace  as  described  is 
shown  in  Fig.  38. 

As  the  furnace  bottom  is  considerably  above  the  ground 
level  a  platform  extends  along  the  front  sufficiently  below 
the  bottom  of  the  working  doors  to  allow  of  ready  manipula- 
tion. The  materials  for  charging  the  furnace  are  brought 
on  to  this  platform  so  that  it  is,  as  a  rule,  very  commodious. 
A  narrower  platform  stretches  along  the  back  of  the  furnace, 
and  below  the  tap  hole ;  this  supports  the  gutter  through 
which  the  metal  runs  when  the  furnace  is  tapped,  and  is 
used  by  the  men  when  breaking  through  the  tap  hole. 

Usually  two  or  more  furnaces  are  built  in  a  row,  and  then 
the  platform  extends  the  full  length  of  the  range.  The 
regenerators  are  below  the  platform,  and  the  valves  for 
regulating  the  gas  and  air  are  worked  by  levers  from  the 
platform,  so  that  the  melter  has  full  control  of  the  gas  and 
air  supply.  The  valves  for  regulating  the  supply  of  gas, 
and  for  reversing  the  course  of  the  gas  and  air,  are  of  two 
kinds.  The  regulating  valve  is  of  the  mushroom  type,  and 
is  raised  and  lowered  from  its  seat  by  a  vertical  rod  actuated 
by  a  lever.  The  reversing  valves  are  of  the  butterfly 
pattern,  and  are  reversed  by  levers.  The  parts  exposed  to 
the  hot  gases  are  water  cooled  to  prolong  their  life.  A 
diagrammatic  sketch  of  the  arrangement  of  flues  at  the 
bottom  of  the  regenerators  is  given  in  Fig.  43. 

The  producers  for  supplying  the  gas  are  built  as  near  as 
possible  to  the  furnaces  they  are  to  supply,  and  are  usually 
of  the  water  bottom  type.  See  p.  40. 

The  regenerators  must  have  a  sufficient  area  of  heating 
surface  for  efficient  working,  and  the  exact  dimensions  of 
the  chambers  are  also  important.  Thus  a  shallow  chamber 


188 


IRON  AND   STEEL. 


THE   OPEN  HEAETH  PEOCESS.  189 

of  a  given  area  of  heating  surface  is  less  efficient  than  a 
deeper  one  of  the  same  area  ;  but  there  is  a  practical  limit 
to  the  depth.  Large  modern  furnaces  require  regenerators 
from  15  to  20  feet  in  depth.  The  usual  ratio  of  the 
dimensions  of  the  gas  and  air  chambers  is  1  to  T37.  A 
separate  chimney  stack  of  sufficient  dimensions  to  cause  a 
strong  draught  is  used  with  each  furnace.  It  is  always 
easy  to  reduce  the  pull  of  the  chimney  by  means  of  a 
damper. 

Auxiliary  chambers  are  sometimes  built  between  the  ports 
and  the  regenerators  to  intercept  as  far  as  possible  the  fine 
particles  of  solid  matter  carried  from  the  furnace  by  the 
escaping  gases.  These  dust  catchers  or  slag  pockets 
increase  the  life  and  facilitate  the  working  of  the  furnace 
by  preventing  the  passages  through  the  regenerators  from 
becoming  choked,  and  the  surface  of  the  brickwork  from 
being  fluxed  by  the  dust  particles.  Also  they  are  a  safe- 
guard in  case  of  the  slag  boiling  over  and  running  down 
the  gas  ports.  See  Fig.  39. 

The  casting  ladle  is  similar  to  the  one  already  described 
(p.  164),  but  is  mounted  on  a  trolley  running  on  rails 
over  the  casting  pit,  which  is  parallel  to  the  back  of  the 
furnace,  or  is  swung  from  an  overhead  crane.  A  good  idea 
of  the  general  appearance  of  an  open  hearth  furnace  is 
given  in  Fig.  40. 

The  Siemens  Process. — The  first  method  introduced  by 
Siemens  consisted  in  melting  pig  iron  practically  free  from 
phosphorus  on  the  bed  of  an  acid  lined  open  hearth,  and  then 
refining  the  metal  by  the  addition  of  good  haematite  ore. 
This  was  known  as  the  pig  and  ore  process,  but  the  results 
were  not  altogether  satisfactory,  for  the  lighter  ore  did  not 
mix  well  with  the  bath  of  metal.  Another  process,  due  to 
Martin,  was  to  melt  the  charge  of  pig  iron,  and  then  to  put 
in  a  large  proportion  of  good  quality  scrap,  which  was 
dissolved  by  the  molten  pig,  and  the  carbon  and  silicon 


IPO  IEON  AND   STEEL. 

distributed  through  the  whole  charge  ;  but  there  was  also 
a  certain  amount  of  refining  due  to  oxide  of  iron  formed  in 
the  furnace  by  the  oxidation  of  a  portion  of  the  charge. 
Again  the  results  were  not  satisfactory,  and  the  present 
open  hearth  process  is  a  combination  of  the  two  ;  for  pig, 
scrap,  and  ore  are  all  used.  This  allows  of  more  regular 
working,  and  more  even  distribution  of  the  charge,  and  is 
better  suited  to  general  furnace  conditions  than  either  of 
the  simpler  processes.  It  is  sometimes  called  the  Siemens- 
Martin  process. 

The  Acid  Process.— H  the  furnace  bottom  is  new,  it  is 
prepared  for  regular  working  by  melting  a  small  charge  of 
pig  iron,  together  with  some  siliceous  material  to  form  slag, 
and  then  raking  the  molten  matter  all  over  the  bed  and  up 
the  sides  so  as  to  well  saturate  them.  The  charge  is  then 
tapped,  and  the  metal  taken  to  the  scrap  heap.  An 
alternate  method,  largely  used  in  America,  is  to  melt  acid 
slag  on  the  bed,  and  well  rabble  it  over  the  sides.  Several 
charges  smaller  than  the  capacity  of  the  furnace  are  then 
worked  off,  gradually  increasing  up  to  the  full  capacity. 

The  proportion  of  pig  and  scrap  in  the  charge  varies 
considerably  in  different  works  according  to  the  quality  of 
the  pig  and  the  quantity  of  scrap  on  hand ;  but  in 
general  practice  from  70  to  80  per  cent,  of  pig  and  20  to  30 
per  cent,  of  scrap  are  used.  The  pig  should  be  non- 
phosphoric,  with  a  moderate  content  of  silicon,  if  good  steel 
is  to  be  produced.  Heavy  scrap  is  also  much  more  satis- 
factory than  light  scrap,  for  the  latter  oxidises  more  freely, 
and  is  much  larger  in  bulk.  The  pigs  are  broken  in  two 
for  convenience,  and  charged  into  the  furnace  first.  In 
order  that  the  charge  may  be  put  in  as  rapidly  as  possible  all 
-  the  three  doors  are  used,  and  at  least  six  men  are  required  for 
the  work.  The  furnace  man  uses  an  iron  tool  called  a  peel. 
He  rests  the  blade  of  the  peel  on  the  step  of  the  door  while 
a  labourer  puts  half  a  pig  on  it,  and  then  shoots  the  metal 


THE  OPEN  HEAETH  PROCESS. 


191 


192  IEON  AND   STEEL. 

on  to  the  bed.  This  is  repeated  until  the  whole  of  the 
charge  is  introduced,  and  the  men  get  so  expert  at  the  work 
that  the  charge  is  evenly  distributed  over  the  bed.  The 
scrap  is  then  put  in,  and  the  furnace  doors  closed.  With 
light  scrap  it  is  sometimes  impossible  to  get  the  whole  in  at 
once,  and  the  remainder  has  to  be  added  as  the  charge 
melts  down.  When  the  furnace  is  charged  and  the  doors 
are  down  the  "  melter,"  as  the  man  in  charge  of  the  furnace 
is  called,  has  very  little  to  do  but  to  see  that  the  furnace  is 
working  properly,  and  to  reverse  the  direction  of  the  air 
and  gas  every  twenty  minutes.  In  about  three  hours  the 
charge  is  quite  molten  and  ready  for  the  addition  of  the  ore. 
Pure  haematite  ore  is  then  thrown  into  the  bath  a  little  at  a 
time,  the  additions  being  so  regulated  as  not  to  cause  the 
bath  to  "  boil  "  too  rapidly,  or  some  of  the  charge  would 
flow  out  of  the  furnace.  During  the  boiling  the  oxygen  of 
the  iron  oxide  added  is  oxidising  the  carbon  in  the  charge 
with  the  formation  of  carbon  monoxide,  and  it  is  the  escape 
of  this  gas  that  causes  the  boil. 

The  carbon  thus  gradually  disappears  from  the  bath, 
and  the  melter  takes  out  samples  from  time  to  time  in  a 
small  ladle  called  a  spoon.  These  are  cast  in  a  round 
mould,  flattened  under  a  hammer,  and  quenched  in  water. 
From  the  appearance  of  the  fractured  surfaces  of  these 
samples  the  condition  of  the  bath  is  judged,  and  more  ore 
added  or  not  as  required.  For  soft  metal  the  carbon  is 
worked  down  to  about  ^  per  cent.  The  silicon  in  the  pig 
is  oxidised  to  silica  and  passes  into  the  slag  in  the  earlier 
stages  of  the  process,  so  that  the  disappearance  of  the 
carbon  indicates  the  end  of  the  refining.  When  the  metal 
is  considered  ready  for  tapping  a  few  lumps  of  pig  are 
thrown  into  the  bath,  just  sufficient  to  keep  it  working,  but 
not  enough  to  appreciably  affect  the  percentage  of  carbon. 
The  bath  is  now  ready  for  the  addition  of  the  ferro- 
manganese,  which  is  either  thrown  into  the  furnace  in 


THE   OPEN  IIEAETH   PROCESS.  1915 

lumps,  or  added  in  a  stream  of  small  pieces  to  the  metal  as 
it  runs  into  the  ladle. 

Fig.  41  shows  the  working  side  of  a  row  of  three  open 
hearth  furnaces,  one  45  tons  and  two  30  tons,  at  Messrs. 
Firth's,  Sheffield. 

Tapping.  —  To  tap  the  furnace  an  iron  bar  tipped  with 
steel  is  driven  with  sledges  through  the  clay  stopping,  and 
then  hammered  back  by  striking  the  inside  of  projections 
on  the  free  end.  When  the  hole  is  free  the  melter  enlarges 
it  from  the  inside  by  thrusting  in  a  pricker  rod  and  working 
it  about.  The  molten  metal  runs  from  the  tap  hole  through 
a  clay  lined  iron  gutter,  previously  made  hot  by  burning 
coal  in  it,  into  the  ladle  placed  underneath  to  receive  it. 
As  the  metal  runs  into  the  ladle  a  small  sample  is  caught 
in  a  spoon,  cast  into  a  small  ingot,  tested  for  weldability  and 
toughness,  and  then  analysed.  A  record  of  each  cast  from 
the  furnace  is  thus  kept. 

The  slag  must  be  kept  sufficiently  fluid  to  protect  the 
metal  while  the  refining  is  in  progress,  and  to  prevent 
trouble  during  the  tapping.  A  thick,  pasty  slag  is  to  be 
avoided,  and  if  it  forms,  a  few  lumps  of  limestone  must  be 
added  to  flux  it  before  the  furnace  is  tapped. 

The  tap  hole  will  give  trouble  if  not  carefully  cleared 
after  each  tapping  and  before  it  is  made  up  with  anthracite 
and  clay  for  the  next  heat.  Should  the  tap  hole  break 
through  during  the  working  of  a  charge,  and  the  ladle 
cannot  be  got  under,  the  metal  must  run  into  the  pit  and 
be  broken  up  for  removal.  Sometimes  the  tap  hole  becomes 
hard  set,  and  a  number  of  rods  and  hard  sledging  are 
required  to  break  through  it.  These  difficulties,  which 
have  to  be  overcome  by  much  labour,  give  rise  to  the  terms 
''break  through"  and  "  hard  tap,"  and  are  among  the 
worries  of  even  the  most  expert  furnace  managers. 

The  ladle,  which  has  already  been  described  in  the 
casting  of  Bessemer  steel,  is  then  brought  over  the  moulds 

j.s.  o 


OF    THE 

UNIVERSITY 

OF 


194 


IRON  AND   STEEL. 


THE   OPEN  HEAETH   PROCESS.  195 

in  the  casting  pit,  and  the  metal  tapped  into  them.  The 
centre  crane  method  of  carrying  the  ladle  is  not  much  used 
in  connection  with  the  open  hearth  as  the  pits  are  usually 
straight.  The  ladle  is  mounted  on  a  carriage  which  can  be 
moved  by  hand  gearing  or  drawn  by  a  locomotive,  and  so 
moved  from  mould  to  mould  on  rails  running  along  the 
sides  of  the  pit.  The  ingots  are  then  stripped  and  removed 
as  soon  as  they  are  sufficiently  set  to  handle.  See  Fig.  33. 
Sometimes  the  ladle  is  suspended  from  an  electric  travelling 
crane  which  runs  parallel  to  the  row  ,of  furnaces,  and  by 
which  it  can  be  brought  into  position  under  any  one 
of  them.  This  arrangement  is  very  suitable  where  the 
system  of  car  casting  is  in  use ;  that  is,  when  the  moulds 
are  placed  on  cars  running  on  rails  at  the  bottom  of  the 
casting  pit,  and  are  drawn  under  the  ladle  one  by  one  to 
receive  the  metal.  The  stripping  of  the  ingots  and  tlieir 
removal  need  not  be  so  hurried  as  in  the  case  of  the 
Bessemer  process,  for  several  hours  intervenes  between  the 
casts  from  a  particular  furnace.  The  stripping  crane 
mostly  used  is  a  "  traveller,"  and  runs  on  rails  outside  the 
pit.  It  is  of  the  locomotive  type  with  a  vertical  boiler. 
Separate  engines  are  used  for  working  the  lifting  portion, 
or  crane  proper,  and  for  moving  the  trolley,  but  it  is  self- 
contained,  and  is  used  for  a  variety  of  purposes.  The 
ingots  are  stripped  by  it,  and  then  carried  to  the  soaking 
pits,  or  re-heating  furnaces. 

Fig.  42  shows  the  casting  ladle  in  position  with  the  end 
of  the  gutter  leading  from  the  tap  hole  directly  over  it. 

Refining  in  the  open  hearth,  which  consists  of  the 
removal  of  silicon  and  carbon  from  the  charge,  is  effected 
in  part  by  the  oxidation  of  a  small  proportion  of  the  iron 
during  the  melting  down,  for  the  atmosphere  in  the  furnace 
is  oxidising  in  character,  and  in  part  by  the  oxygen  from 
the  rich  oxide  added  to  cause  the  boil.  Pig  iron  too  high 
in  manganese  is  objectionable,  as  that  metal  exerts  a 

o  2 


196 


IEON  AND   STEEL. 


corrosive  action  on  the  sides  of  the  bed,  and  makes  the  slag 
too  thin.  Phosphorus  and  sulphur  are  not  removed  at  all 
in  the  refining  on  a  silica  bed,  and  will  be  slightly  higher 
in  the  finished  metal  than  in  the  original  charge.  This 
necessitates  careful  selection  of  the  pig,  scrap,  and  ore  if 
high-class  metal  is  to  be  produced.  The  following  table 
gives  a  general  idea  of  the  character  of  the  pig,  scrap,  and 
finished  metal : — 


Carbon 
per  cent. 

Silicon 
per  cent. 

Manganese 
per  cent. 

Phosphorus 
per  cent. 

Sulphur, 
per  cent. 

General  limits 

3  to  3-6 

1-9  to  2-5 

0-7  to  0-9 

0'03  to  0'04 

0-02  to  0-04 

Suitable  pig   . 
Scrap  metal    . 

3-5 
0-2 

Variable, 

2-25 
0-04 

0-80 
0-5 

0-035 
0-04 

0-03 
0-04 

Finished  steel 

but  under 

0-03 

0-5 

O'Oo 

0-05 

control. 

The  slag  contains  an  excess  of  silica,  and  is,  therefore, 
acid  in  character.    The  following  is  a  typical  composition  : — 


ACID  OPEN  HEARTH  SLAG. 


Silica,  Si02 
Ferrous  oxide,  FeO 
Manganous  oxide,  MnO 
Lime,  CaO 
Alumina,  A1203     . 
Magnesia,  MgO    . 


57-0 
25-0 
8-0 
5-5 
3'5 
I'O 

lOO'O 


In  making  acid  open  hearth  steel  all  the  materials  must 
be  of  the  best,  and  as  free  as  possible  from  impurities  not 
removed  in  the  furnace.  On  that  account  the  steel 
produced  commands  a  good  price.  The  percentage  of 


THE   OPEN  IIEAETH  PEOCESS.  197 

carbon  can  be  controlled  within  fairly  wide  limits,  and  high 
carbon  steels  produced.  The  metal,  however,  is  not  quite 
suitable  for  the  best  cutting  tools,  and  only  a  small 
proportion  is  used  for  that  purpose.  The  description  of  the 
process  given  above  refers  to  the  production  of  "  dead 
soft "  steel,  or  more  correctly  high-class  ingot  iron. 
When  higher  carbon  steels  are  to  be  made  the  process  is 
modified  at  the  finish  so  as  to  introduce  the  necessary 
content  of  carbon.  This  may  be  done  in  several  ways  ; 
(1)  by  finishing  the  refining  when  the  carbon  is  reduced  to 
the  proper  percentage,  and  then  tapping  the  metal ;  (2)  by 
refining  the  charge  until  nearly  all  the  carbon  is  removed, 
and  then  working  it  back  by  the  addition  of  pure  pig  or 
spiegel,  or  both ;  (3)  by  refining  until  nearly  all  the  carbon 
has  disappeared,  and  then  adding  the  required  carbon  to 
the  ladle.  In  making  axle-steel,  which  usually  contains 
less  than  0*5  per  cent,  of  carbon,  the  first  method  is  often 
adopted,  but  the  process  must  be  conducted  with  care.  The 
addition  of  the  ore  is  so  regulated  that  when  the  carbon  has 
been  brought  down  to  the  proper  content  the  slag  is  free 
from  active  oxidising  bodies.  If  not,  the  composition  of 
the  bath  will  be  disturbed  on  the  addition  of  the  ferro- 
manganese,  for  carbon  would  be  removed  by  the  action  of 
the  slag. 

For  higher  carbon  steel  the  bath  is  worked  down  to 
about  0*2  per  cent,  carbon,  and  then  brought  back  by  the 
addition  of  pure  pig  iron  and  spiegel.  These  bodies  are 
placed  on  the  banks  of  the  hearth,  where  they  melt  down 
and  run  into  the  bath  of  metal  carrying  in  the  necessary 
carbon  and  manganese.  Even  more  care  must  be  taken  to 
have  the  slag  non-oxidising,  and  not  too  thin.  The  per- 
centage of  carbon  in  the  metal  can  be  determined  by 
dipping  out  a  small  sample  with  a  "  spoon,"  and  comparing 
it  with  a  standard  steel  by  the  Eggertz  colour-test,  which 
only  requires  a  few  minutes  to  complete. 


198  IRON  AND   STEEL. 

The  method  of  introducing  the  carbon  in  the  ladle  is 
also  largely  used.  Mr.  Darby,  of  Brymbo,  invented  a 
process  for  the  rapid  carburization  of  steel  by.  running  the 
molten  metal  through  a  layer  of  charcoal  contained  in  a 
perforated  tube.  In  this  way  he  increased  the  content  of 
carbon  in  a  charge  of  metal  from  0'2  to  1  per  cent.,  and 
found  that  the  amount  taken  up  depended  on  the  depth  of 
the  layer  through  which  the  metal  had  to  pass. 

It  was  found,  however,  that  much  the  same  thing  could 
be  effected  by  adding  charcoal  to  the  ladle,  as  the  carbon  is 
taken  up  rapidly  by  the  metal.  The  method  now  largely 
adopted  is  to  place  the  charcoal  in  paper  bags  and  throw 
them  into  the  ladle  at  intervals.  The  first  bag  is  thrown 
in  when  the  metal  just  covers  the  bottom  of  the  ladle. 
Another  method  is  to  feed  in  the  charcoal  through  a  hopper 
fixed  vertically  over  the  casting  ladle  while  the  metal  is 
being  tapped  into  it.  About  half  the  carbon  put  into  the 
ladle  is  taken  up  by  the  metal,  and  the  process  seems  to 
give  very  accurate  results.  In  one  American  steel  works 
twenty-four  casts  were  made,  and  the  greatest  difference 
from  the  desired  content  of  carbon  in  the  whole  series  was 
0*02  per  cent.  A  considerable  saving  of  ferro-manganese 
and  spiegeleisen  is  thus  effected. 

The  Bessemer  converter  and  the  open  hearth  furnace 
are  sometimes  used  in  combination.  When  the  metal  has 
been  blown  until  nearly  the  whole  of  the  silicon  and  part 
of  the  carbon  have  been  removed  two  charges  from  the 
converters  are  run  into  an  open  hearth,  sampled  for 
carbon,  ore  added  to  produce  the  boil,  and  the  charge 
finished  and  tapped. 

Basic  Open  Hearth  Practice. — Although  it  was  thought 
to  be  practically  impossible  to  remove  the  whole  of  the 
phosphorus  from  a  charge  of  phosphoric  pig  iron  without 
the  use  of  a  blast  of  air,  it  has  not  proved  so  in  the  sequel, 
and  highly  phosphoric  pig  can  be  treated  in  the  open 


THE   OPEN  HEARTH  PROCESS.  199 

hearth  without  the  aid  of  more  air  than  passes  through  the 
furnace  in  the  ordinary  course. 

The  details  of  the  furnace  used  for  the  basic  process  are 
very  similar  to  those  already  described  for  the  acid-lined 
furnace.  The  main  difference  is  in  the  bed  lining,  which 
must  be  basic  in  character,  and  burnt  dolomite  is  the  best 
material  for  the  purpose.  As  is  generally  the  case,  more 
modifications  in  the  construction  of  the  furnaces  used  in 
the  early  basic  practice  were  introduced  than  were  necessary 
for  successful  working  ;  and  in  modern  basic  practice  the 
furnace  is  very  similar  to  that  used  for  the  acid  process, 
except  in  the  hearth  lining.  Theoretically  the  walls  and 
roof  of  a  basic  furnace  should  be  lined  with  basic  materials  ; 
but  this  is  impossible,  as  basic  bricks  break  down  so 
readily  that  they  cannot  be  used  for  the  roof  and  walls. 
It  is  found,  however,  that  the  fluxing  tendency  of  good 
silica  bricks  when  in  contact  with  dolomite  lime  is  not 
nearly  so  great  as  might  be  expected,  even  at  the  high 
temperature  of  the  open  hearth,  especially  if  they  are  not 
subjected  to  much  pressure  where  they  are  in  contact;  so 
that  only  ordinary  precautions  need  be  taken,  and  the  roof 
and  walls  constructed  of  silica  bricks  in  the  usual  way.  A 
layer  of  some  neutral  material,  such  as  chrome  iron  ore, 
may  be  used  to  separate  the  two  where  they  would  come 
into  contact,  and  the  liability  to  fluxing  thus  greatly 
reduced. 

The  Batho  furnace  was  one  of  the  earliest  in  use  for 
basic  work,  and  it  was  in  the  construction  of  this  furnace 
that  the  regenerators  were  first  built  independently  of  each 
other  and  quite  separate  from  the  furnace.  It  was  claimed 
for  this  arrangement  that  there  was  no  danger  of  gas  and 
air  firing  between  the  two  regenerators,  and  that  no  damage 
could  be  done  to  them  in  case  of  a  break  through  of  metal 
from  the  bed.  The  bed  was  round,  and  the  roof,  which 
was  independent  of  the  rest  of  the  furnace,  was  suspended 


200  IRON  AND   STEEL. 

from  girders  overhead  so  that  it  could  be  raised  for  repairs. 
Messrs.  Eiley  and  Dick,  and  others,  have  modified  the 
construction  of  this  furnace  in  various  ways,  but  it  has  not 
come  into  general  use,  for  the  modern  basic  furnace  is 
essentially  the  Siemens  open  hearth. 

Various  methods  are  adopted  in  the  construction  of  the 
side  walls  and  roof,  and  in  the  lining  of  the  hearth.  The 
following  may  be  taken  as  the  most  general,  and  is  largely 
due  to  Mr.  Darby,  of  Brymbo.  The  roof  of  silica  bricks  is 
carried  on  a  horizontal  arch  so  that  there  shall  not  be  much 
pressure  between  the  brickwork  of  the  side  walls  and  the 
basic  material  of  the  hearth  where  they  come  into  contact. 
A  chrome  ore  joint  may  thus  be  dispensed  with.  The 
bottom  plates  are  covered  with  a  layer  of  silica  bricks,  and 
then  basic  bricks  are  built  round  the  sides  of  the  hearth  to 
help  to  form  the  banks.  Dolomite  lime  mixed  with  tar  is 
rammed  all  over  the  bottom  and  well  burnt  on  ;  then  more 
dolomite  lime  is  spread  over  and  glazed  on  an  inch  at  a 
time  until  the  bed  is  complete.  In  this  way  a  good  durable 
bed  is  formed  with  the  tops  of  the  banks  well  above  the 
slag  line.  Dolomite  lime  although  very  refractory  is  just 
fusible  enough  to  frit  at  the  temperature  of  a  Siemens 
furnace.  This  is  probably  due  to  the  small  quantity  of 
silica  it  contains  forming  a  fusible  double  silicate  of  lime 
and  magnesia  in  sufficient  quantity  to  slightly  soften  the 
mass.  Pure  lime  does  not  frit,  so  cannot  be  used  in  place  of 
dolomite.  Unless  the  bed  is  well  formed  as  described, 
portions  of  it  may  break  away  during  working  and  rise 
through  the  bath  of  metal.  The  tap  hole  is  formed  in  a 
similar  manner  to  that  already  described  for  the  acid  open 
hearth. 

Working  a  Charge. — The  furnace  being  hot  and  ready 
for  charging,  some  lime  and  iron  ore  are  first  placed  on  the 
bed,  and  then  the  pig  is  charged  with  the  addition,  from 
time  to  time,  of  more  lime  and  ore ;  finally  the  scrap  is 


THE  OPEN  HEARTH  PROCESS.  201 

added.  When  the  charge  has  melted  down  and  become 
quite  clear,  non-siliceous  iron  ore,  or  basic  reheating  furnace 
cinder  free  from  silica,  is  added  together  with  lime,  these 
additions  being  made  from  time  to  time  as  required. 
The  melter  watches  the  boil  carefully  and  takes  out  small 
samples,  which  are  hammered  out,  quenched  and  fractured. 
From  the  appearance  of  the  fracture  he  is  able  to  judge  of 
the  extent  to  which  the  phosphorus  has  been  removed. 
The  sufficient  removal  of  the  phosphorus  is  the  sine  qua  non 
of  the  process,  which  is  not  complete  until  the  phosphorus 
has  been  brought  down  to  0*05  per  cent,  or  less.  The 
information  obtained  from  the  appearance  of  the  fracture  is 
sometimes  checked  by  the  rapid  estimation  of  the  phos- 
phorus in  the  sample.  The  chief  aim  of  the  melter  is  to 
keep  the  bath  on  the  boil  until  the  phosphorus  is  brought 
down  sufficiently ;  but  as  the  boil  ceases  when  the  carbon 
has  gone,  its  too  rapid  removal  must  be  guarded  against. 
Should  the  boil  moderate  too  rapidly  the  temperature  must 
be  regulated  and  pig  iron  added  to  prolong  the  action.  The 
boil  is  caused  by  the  rapid  escape  of  carbon  monoxide 
due  to  the  oxidation  of  the  carbon  in  the  bath.  This 
agitates  the  molten  mass  and  brings  the  metal  well  into 
contact  with  the  oxidising  bodies  and  the  lime.  The 
phosphorus  is  thus  oxidised,  and  the  phosphoric  oxide 
formed  unites  with  the  lime  to  form  a  phosphate  of  lime, 
which  passes  into  the  slag. 

When  the  melter  is  satisfied  that  the  phosphorus  is  low 
enough  and  the  carbon  is  right,  a  little  haematite  pig  is 
thrown  in  and  the  charge  is  ready  for  tapping.  The  tap 
hole,  which  is  made  up  from  the  inside  with  anthracite 
as  in  the  acid  process,  and  from  the  outside  with  dolomite 
lime  and  tar  instead  of  clay,  is  broken  through  in  the  usual 
manner,  and  the  metal  tapped  into  the  ladle.  The  neces- 
sary ferro-manganese  in  small  pieces  is  allowed  to  fall 
into  the  stream  of  metal  as  it  runs  from  the  furnace.  A 


202 


IKON  AND   STEEL. 


general    idea   of  the  composition  of   the    pig,  scrap,    and 
finished  metal  is  given  by  the  following  table  :  — 


Carbon 
per  cent. 

Silicon 
per  cent. 

Manganese 
per  cent. 

Phosphorus 
per  cent. 

Sulphur 
per  cent. 

General  limits 

3"25to3'7o 

0-5  to  1-0 

1-5  to  2 

0-1  to  2-5 

O-OTtoO-Oo 

Suitable  pig  . 

3-5 

0-8 

2-0 

I'd 

0-05 

Scrap  metal    . 

Variable. 

0-06 

0-1 

0-05 

Variable, 

Finished  steel 

but  under 

0-06 

0-06 

O'Oo 

0-05 

control. 

The  Slay  contains  an  excess  of  phosphate  of  lime,  and  a 
typical  analysis  is  given  below. 


Basic  Open  Hearth  Slag. 

Silica,  Si02 

Oxide  of  Iron,  Fe203 

Phosphoric  Oxide,  P205 

Manganous  Oxide,  MnO 

Lime,  CaO     . 

Magnesia,  MgO       .... 


12 
17 
14 
10 

42 
5 

100 


The  important  points  to  be  noticed  in  the  working  of  the 
basic  process  are  connected  with  the  permanent  removal 
of  the  phosphorus.  In  basic  Bessemer  practice  the  phos- 
phorus is  an  important  heat  producer,  and  is  necessary  to 
the  conduct  of  the  process  ;  but  in  the  open  hearth  the 
heat  required  to  carry  on  the  refining  is  very  largely  pro- 
duced by  the  combustion  of  the  external  gases.  Therefore, 
pig  iron  low  in  phosphorus,  which  would  probably  give  an 
unsatisfactory  blow  in  the  Bessemer  converter,  can  be  dealt 
with  readily  in  the  open  hearth.  As  a  matter  of  fact,  an 


THE   OPEN  HEAETH  PEOCESS.  203 

iron  too  high  in  phosphorus  is  difficult  to  deal  with,  as  the 
carbon  may  be  all  removed  before  the  phosphorus  is  low 
enough,  and  thus  cause  trouble.  But  with  care  all  grades 
of  phosphoric  pig  may  be  used.  Also,  the  scrap  used  in 
the  process  may  contain  more  phosphorus  than  would  be 
admissible  in  the  acid  process,  and  on  that  account  is  often 
cheaper. 

High  silicon  pig  is  usually  low  in  sulphur,  and  thus  pro- 
duces good  metal ;  but  it  should  have  its  silicon  reduced 
before  being  put  into  the  basic  hearth.  An  easy  way  of 
doing  this  is  to  blow  the  metal  for  a  few  minutes  in  an 
acid  lined  converter  ;  but  this  means  waste  of  metal  and  the 
maintaining  of  two  plants  which  may  more  than  balance 
the  extra  cost  of  selected  pig.  The  late  Sir  I.  L.  Bell  intro- 
duced a  "washing"  process  by  which  silicon  can  be  largely 
removed  and  phosphorus  considerably  reduced  by  acting 
upon  the  metal  with  a  strongly  oxidising  slag  at  a  moderate 
temperature.  See  p.  137. 

The  relation  of  the  slag  to  the  bath  of  metal  is  also  very 
important,  for  although  the  phosphate  of  lime  formed  is 
stable  at  the  temperature  of  the  furnace,  it  is  reduced  by 
carbon  at  that  temperature,  and  the  reduced  phosphorus 
passes  back  into  the  metal.  The  slag  must  be  sufficiently 
basic,  and  silica  should  not  be  allowed  to  accumulate  in 
it,  as  silica  is  able  to  replace  phosphoric  oxide,  which 
is  then  more  readily  reduced  by  carbon.  On  this  account 
care  must  be  exercised  in  the  additions  made  to  the  charge 
at  the  end  of  the  boil.  For  example,  it  is  impossible  to  put 
in  haematite  pig,  as  in  the  method  of  "pigging  back" 
already  described  in  the  acid  process,  except  in  small  quan- 
tities, for  the  carbon  this  introduced  would  reduce  phosphate 
in  the  slag,  and  the  reduced  phosphorus  would  pass  back 
into  the  metal.  Also,  the  ferro-manganese  must  be  put 
into  the  ladle  and  not  into  the  furnace,  and  the  slag  must 
be  kept  out  of  the  ladle  as  far  as  possible. 


204  IEON  AND  STEEL. 

Most  of  the  basic  steel  produced  is  low  in  carbon ;  but 
high  carbon  metal  can  be  made  by  putting  carbon  into  the 
ladle.  The  simple  bag  method  has  already  been  described, 
but  in  the  opinion  of  some  authorities  more  uniform  results 
are  obtained  by  feeding  in  the  ground  anthracite  from  a 
hopper  suspended  over  the  ladle  on  to  the  metal  while  it  is 
being  tapped  from  the  furnace.  The  proportion  of  carbon 
absorbed  to  that  added  depends  upon  the  quantity  it  is 
desired  to  introduce  into  the  metal.  The  higher  the  per- 
centage of  carbon  in  the  finished  steel  the  smaller  the 
proportion  of  the  added  carbon  that  is  absorbed.  The 
quantity  absorbed  seems  to  vary  from  J  to  j  of  that 
added. 

Silicon  is  readily  removed  in  the  furnace,  but  it  is  not 
desirable  to  use  pig  containing  much  silica,  as  this  would 
cause  an  accumulation  of  silica  in  the  slag,  which,  as  already 
indicated,  is  to  be  avoided. 

The  presence  of  sulphur  in  the  pig  is  objectionable  if  low 
sulphur  metal  is  to  be  produced,  for  the  removal  of  that 
element  in  the  process  is  more  or  less  erratic,  and  certainly 
not  under  control.  The  presence  of  manganese  in  the 
charge  facilitates  the  removal  of  sulphur,  but  its  action  is 
limited.  The  elimination  of  sulphur  has  received  much 
attention,  and  various  methods  have  been  proposed  to 
effect  this.  The  conditions  seem  to  be  a  highly  basic  and 
very  fluid  slag.  The  fluidity  of  the  slag  is  usually  increased 
by  the  addition  of  calcium  chloride,  CaCl2,  and  fluor-spar, 
CaF2.  Both  these  compounds  are  recommended  by  Saniter, 
whose  process  is  the  one  most  largely  used.  In  the  basic 
open  hearth  or  Bessemer  process  the  desulphurisers  may 
be  added  to  the  molten  charge  in  the  furnace  or  converter, 
and  the  lime  increased  to  upwards  of  50  per  cent,  in  the 
slag;  but  the  time  required  for  working  the  charge  is 
increased.  This  is  regarded  by  some  makers  with  disfavour, 
as  it  reduces  the  output  of  a  given  furnace ;  but  if  sufficient 


THE   OPEN  HEARTH   PROCESS. 


calcium  chloride  is  added  to  keep  the  slag  very  fluid  to  the 
finish,  this  need  not  be  a  serious  objection.  The  addition 
could  not  be  made  in  the  case  of  acid  lined  apparatus,  as  a 
basic  slag  is  then  quite  inadmissible  ;  but  this  difficulty  can 
be  overcome  by  running  the  molten  metal  from  the  blast 


FIG.  43. — Diagram  of  a  Campbell  Tilting  Furnace  (longitudinal 
and  vertical  section). 

H,  Hearth. 


A,  Air  regenerator. 
D,  Working  doors. 
G,  Gas  regenerator. 


w,  Waste  gas  culvert. 


furnace  or  mixer  into  a  ladle  on  the  bottom  of  which  a 
mixture  of  calcium  chloride,  fluor-spar,  and  lime  has  been 
placed.  The  mixture  melts,  rises  through  the  metal,  and 
removes  upwards  of  50  per  cent,  of  the  sulphur  present. 
The  desulphurised  metal  may  then  be  cast  into  pigs,  or  it 
may  be  run  direct  into  the  converter. 

Tilting  Furnaces. — One  of  the  most  important  advances 


206  IRON  AND   STEEL. 

in  open  hearth  practice  is  marked  by  the  introduction  of 
the  tilting  furnace.  This  furnace  does  not  differ  in  any 
essential  from  the  Siemens  furnace.  It  is  usually  larger 
than  the  ordinary  type,  and  the  body  is  movable,  so  that 
either  the  charging  side  or  the  tapping  side  can  be  tilted 
down  as  required.  There  are  two  systems  by  which  the 
rotary  motion  is  given  to  the  furnace  body.  In  the  Campbell 
type  the  body  rotates  round  its  longitudinal  axis  on  sets  of 
rollers  moving  over  the  segment  of  a  circle  at  each  end. 
The  tilting  is  produced  by  a  hydraulic  ram  working  in  a 
horizontal  cylinder.  In  the  Wellman  type  the  body  is  sup- 
ported on  rockers,  and  can  be  moved  through  the  required 
angle  by  a  ram  working  in  a  vertical  cylinder.  These 
furnaces  are  usually  of  large  size,  ranging  in  hearth 
capacity  from  40  to  600  tons  of  molten  metal.  In  some  of 
the  large  steel  works  in  America  as  many  as  twelve  50-ton 
furnaces  are  at  work.  The  largest  furnaces  of  the  tilting 
type  are  usually  constructed  for,  and  used  as,  metal 
mixers,  and  several  are  now  in  use  in  this  country.  A 
modified  Wellman  furnace  of  200  tons  capacity  is  being 
used  at  the  Eound  Oak  Steel  Works,  Brierley  Hill,  and 
another  of  the  same  capacity  at  the  Spring  Vale  Iron 
Works,  Bilston.  They  are  not  only  useful  as  mixers,  but  a 
certain  amount  of  refining  may  be  effected  in  them.  Thus 
by  the  introduction  of  manganiferous  material  into  the  bath, 
sulphur  may  be  partly  eliminated  as  manganous  sulphide, 
MnS,  in  the  slag.  Also,  some  silicon  would  be  oxidised  as 
the  result  of  the  metal  being  exposed  to  an  oxidising  atmo- 
sphere in  the  furnace,  and  to  an  oxidising  slag.  These 
mixer-furnaces  are  used  with  both  Bessemer  and  fixed 
open  hearth  plants.  Fig.  43  shows  the  Campbell  tilting 
furnace  in  vertical  section.  It  is  seen  that  the  body  is 
quite  independent  of  the  fixed  ends  which  carry  the  flues, 
so  that  it  can  be  rotated  without  interfering  with  the  course 
pf  the  gases  through  it.  The  manner  in  which  the  gases 


THE   OPEN  HEAETH  PROCESS. 


207 


circulate  through  the   system   is   clearly  shown,  but    the 
arrangement  must  be  regarded  as  diagrammatic. 

The  mechanical  appliances  for  handling  the  charges 
worked  in  these  large  furnaces  correspond  to  the  furnaces 
themselves.  The  electric  charger  designed  by  \Vellman  is  one 
of  the  latest  forms  of  mechanical  charging  apparatus.  Its 
position  and  general  appearance  is  indicated  by  B,  Fig.  44. 


FIG.  44. — Diagram  of  a  Campbell  Tilting  Furnace  (cross  section). 
A,  Hydraulic  cylinder.  D,  Casting  ladle. 


B,  Electric  charger. 
c,  Travelling  cranes. 


E,  Hydraulic  ram. 


The  body  of  the  machine  is  mounted  on  wheels  so  that 
it  can  travel  along  the  platform  in  front  of  the  furnace. 
The  horizontal  charger  bar  has  three  distinct  motions : 
it  can  be  moved  to  and  fro  in  the  direction  of  its  length  ; 
it  can  be  raised  and  lowered  vertically ;  or  it  can  be  rotated 
round  its  own  axis.  The  iron  charging  box,  which  contains 
the  solid  materials  to  be  charged  into  the  furnace,  is 
supported  on  a  bogie  carriage  running  on  rails  between  the 


208  IEON  AND   STEEL. 

charger  and  the  furnace,  and  is  readily  brought  in  front  of 
the  door.  At  one  end  of  the  box  there  is  a  socket  into 
which  the  end  of  the  charger  bar  fits,  and  with  which  it  is 
readily  locked  or  unlocked  by  a  rod  running  through  the 
centre  of  the  bar,  and  under  the  control  of  the  operator  at 
the  back  of  the  machine.  The  box  can  thus  be  raised  from 
the  bogie,  thrust  into  the  furnace,  its  contents  tipped  out, 
and  rapidly  withdrawn.  The  travel  of  the  machine  and 
the  movements  of  the  bar  are  brought  about  by  electric 
motors  fixed  to  the  body.  When  the  furnace  is  used  for  a 
mixer  the  molten  metal  is  brought  from  the  blast  furnace 
in  a  ladle,  which  is  then  raised  to  the  platform  by  an 
electric  travelling  crane,  and  its  contents  run  through  a 
gutter  into  the  furnace  by  way  of  the  charging  door.  The 
furnace  is  tilted  when  either  metal  or  slag  is  to  be  run  from 
it.  The  general  arrangement  of  the  tilting  apparatus  is 
shown  in  Fig.  44. 

The  original  form  of  mixer  can  scarcely  be  called  a 
furnace ;  it  is  more  of  the  nature  of  a  very  large  ladle  or 
reservoir,  and  was  called  into  existence  by  the  demand  for 
uniform  fluid  metal  for  the  Bessemer  process.  It  is  either 
rectangular  or  semi-cylindrical  in  form,*  and  the  body  is 
made  of  wrought  iron  plates,  strongly  braced  together,  and 
lined  with  firebricks.  It  is  mounted  so  that  it  can  be  tilted 
in  either  direction  by  means  of  a  hydraulic  ram.  The 
molten  metal  from  the  blast  furnace  is  brought  up  to  the 
mixer  in  a  tilting  ladle,  and  run  in  on  one  side,  while  the 
molten  metal  for  the  Bessemer  charge  is  run  into  a  tilting 
ladle  from  the  other  side.  By  the  tilting  arrangement  the 
outlet  is  brought  below  the  surface  of  the  metal  when  a 
charge  is  to  be  withdrawn,  and  raised  again  when  the  required 
amount  of  metal  has  been  run  into  the  ladle.  The  surplus 
heat  of  the  metal  that  is  run  in  is  supposed  to  keep  the 
temperature  of  the  mixer  above  the  melting  point,  and  this 
is  so  when  a  steady  supply  of  metal  from  the  blast  furnaces 


THE  OPEN  HEARTH  PROCESS.  209 

is  available.  But  the  gas-fired  mixer  is  taking  the  place 
of  the  simple  form,  as  it  is  more  under  control,  and  a  pre- 
liminary refining  can  be  effected  in  it. 

The  Talbot  Process. — There  have  been  several  modifica- 
tions of  the  Siemens-Martin  process  introduced,  and  mostly 
with  the  object  of  shortening  the  time  of  working  off  a 
charge.  As  already  stated,  when  cold  pig  and  cold  scrap 
are  charged,  what  with  repairing  the  bed  and  making  up 
the  tap  hole,  it  is  seldom  that  more  than  two  heats  are 
taken  from  the  same  furnace  in  twenty-four  hours.  Thus 
anything  like  a  steady  supply  of  ingots  straight  to  the  mill 
is  out  of  the  question.  Mr.  B.  Talbot  has  introduced  a 
more  continuous  process,  which  was  first  used  in  America, 
but  is  now  in  use  in  this  country.  The  principle  of  the 
process  is  to  run  a  quantity  of  molten  pig  iron  into  a  bath 
of  already  refined  metal,  and  then  to  work  the  bath  to  the 
finish  again.  A  regulated  proportion  of  this  finished  metal 
is  tapped  from  the  furnace,  and  the  usual  addition  to 
prepare  the  steel  for  casting  added  to  it  in  the  ladle. 

The  process  can  be  worked  in  a  fixed  furnace  of  large 
capacity,  but  a  tilting  furnace  is  much  more  readily  handled, 
and  probably  gives  better  results  than  would  be  obtained 
with  the  same  metal  in  a  fixed  one.  The  Wellman  furnace 
is  generally  used,  but  this  is  not  because  it  is  superior  to 
the  Campbell  furnace  for  general  work.  It  costs  less  to  con- 
struct. About  60  tons  seems  to  be  the  lower,  and  200  tons 
the  higher,  limit  of  capacity  for  the  furnaces  used  in  the 
Talbot  process.  The  Wellman  furnace,  as  used  for  this 
process,  has  a  deep  bed,  and  the  ports  can  be  moved  back 
a  little  when  the  body  is  to  be  tilted,  and  far  enough  back 
for  a  man  to  get  between  when  repairs  are  required.  The 
joints  between  the  ports  and  the  furnace  are  made  by  water 
blocks.  The  slag  can  be  run  either  from  the  charging  or 
the  tapping  side  of  the  furnace. 

The  following  is  the  description   of   the  working  of  a 

i.s.  p 


210  IKON  AND   STEEL 

60-ton  charge :  the  furnace  being  ready,  30  tons  of  molten 
pig  is  run  in,  and  30  tons  of  scrap  added.  The  charge  is 
then  worked  for  steel  in  the  usual  way  by  the  addition  of 
ore  and  lime  in  the  case  of  the  basic  process.  One-third 
of  the  charge  is  then  poured  into  the  ladle  by  tilting  the 
hearth,  and  two-thirds  left  in  the  furnace.  The  run  metal 
is  then  finished  by  the  addition  of  ferro-manganese  to  the 
ladle.  As  soon  as  the  required  quantity  has  been  run  off 
the  hearth  is  brought  back  and  crushed  oxide  of  iron  added 
to  enrich  the  slag  which  is  not  run  off  after  this  first  heat. 
When  the  slag  is  thoroughly  molten  again  a  charge  of  20 
tons  of  molten  pig  is  run  in.  This  causes  a  very  energetic 
action  in  the  bath,  during  which  the  gas  is  shut  off,  much 
carbon  monoxide  is  given  off,  and  the  metal  boils  up.  The 
oxygen  is  furnished  by  the  oxide  added  to  the  slag,  and 
sufficient  heat  is  generated  by  the  oxidation  to  keep  up  the 
temperature  of  the  bath.  In  about  fifteen  minutes  the  slag 
becomes  normal  again,  and  part  of  it  is  run  off  through  a 
tap  hole  by  tilting  the  hearth.  When  the  quantity  of  slag 
has  been  sufficiently  reduced  the  hearth  is  tilted  back  and 
the  slag  hole  made  up.  The  gas  is  then  turned  on,  the 
bath  worked  to  steel  by  the  addition  of  ore  and  lime  as 
before,  and  20  tons  tapped  into  the  ladle  to  be  finished  as 
usual.  The  sides  of  the  bed  at  the  slag  line  are  examined 
and  made  up,  if  necessary,  and  the  process  exactly  repeated. 
The  interval  between  the  casts  is  about  four  hours.  The 
furnace  is  worked  as  described  for  a  week,  and  it  is  said 
that  thirty-two  casts  can  be  made  in  that  time  when  the 
molten  pig  is  taken  from  a  mixer.  Thus  the  output  of  a 
single  furnace  is  upwards  of  600  tons  of  steel  ingots  per 
week  in  a  fairly  continuous  stream  to  the  mill.  By  using 
furnaces  with  a  greater  capacity,  and  tapping  a  smaller 
proportion  of  the  total  charge,  the  time  between  the  casts 
can  be  still  further  reduced  to  about  one  hour. 

When  the  furnace  is    shut   down  at  the  week-end  the 


THE   OPEN  HEAETH   PROCESS.  211 

whole  of  the  last  charge  is  tapped,  and  the  bed  thoroughly 
repaired  ready  for  the  next  week's  campaign.  One  of  the 
advantages  of  the  process  is  that  the  greater  part  of  the  bed 
is  covered  with  molten  metal,  which  has  little  or  no  corrosive 
action  on  the  lining.  In  fact,  the  corrosive  wear  is  mostly 
confined  to  the  slag  line,  although  there  is  the  constant 
mechanical  wear  due  to  the  large  body  of  metal  on  the 
bed. 

A  Talbot  plant  with  a  100-ton  furnace  is  in  use  at 
Frodingham,  and  a  still  larger  furnace  at  the  works  of 
Messrs.  Guest,  Keen  &  Co.,  Cardiff.  In  America  200- ton 
furnaces  are  used  in  the  same  process. 

According  to  Professor  Harbord,  there  is  an  important 
future  for  this  process  in  the  treatment  of  good  haematite 
pig  taken  from  a  mixer  and  worked  on  a  basic  bed.  He 
says  that  in  this  way  a  very  uniform  steel  of  excellent 
quality  can  be  produced,  for  the  silicon  is  rapidly  oxidised, 
and  there  is  very  little  phosphorus  to  be  removed,  so  that 
the  metal  can  be  finished  without  working  down  the  carbon 
to  the  limit. 

The  Bertrand-Thiel  Process. — This  is  another  open 
.hearth  process  which  has  for  its  object  the  saving  of  time 
and  the  more  regular  supply  of  ingots  to  the  mill.  It  is  a 
double  furnace  method,  and  is  adapted  to  the  use  of  molten 
pig  direct  from  a  mixer.  The  charge  of  molten  pig  is  run 
on  to  the  bed  of  the  first  furnace,  which  already  contains 
iron  ore  and  lime,  and  is  partly  refined  by  the  action  of 
these  substances.  The  phosphorus  is  brought  down  to 
O'l  per  cent.,  while  there  is  still  2  per  cent,  of  carbon  left 
in  the  charge,  which  is  amply  sufficient  for  the  final  boil. 
The  partly  refined  metal  is  then  transferred  to  the  second 
furnace,  which  contains  ore,  lime,  and  scrap  already  at  a 
sweating  heat.  The  full  charge  is  then  melted  and  finished 
ready  for  tapping. 

A  shallow  bath  of  metal  is  required  for  rapid  refining,  so 

p  2 


212  IRON  AND   STEEL. 

that  the  furnaces  must  have  a  much  larger  bed  area  than 
is  necessary  for  the  ordinary  open  hearth  process.  Also 
the  wear  is  greater  on  account  of  the  cutting  action  of  the 
molten  metal.  The  latter  is  reduced,  however,  by  the 
presence  of  the  ore  and  lime  on  the  bed  when  the  metal 
is  run  in.  The  time  in  the  first  furnace  is  four  hours,  and 
in  the  second  two  hours  ;  but  as  the  furnaces  are  working 
jointly  five  casts  can  be  made  in  twenty-four  hours.  The 
metal  from  the  first  furnace  is  either  run  through  a  gutter 
direct,  or  tapped  into  a  ladle  and  then  run  into  the  second 
furnace.  In  running  direct  the  bed  of  the  first  furnace 
must  be  at  a  higher  level  than  that  of  the  second. 

This  process  is  being  successfully  worked  at  the  Earl  of 
Dudley's  steel  works,  Eound  Oak.  It  is  said  that  the 
second  furnace  is  unnecessary,  and  that  the  steel  can  be 
finished  in  the  same  furnace.  To  do  this  the  partially 
refined  metal  is  tapped  from  the  furnace  into  a  ladle,  the  ore, 
lime,  and  scrap  charged  at  once,  and  the  molten  metal  run 
back  to  be  finished.  The  advantage  of  tapping  the  partially 
finished  metal  and  then  running  it  back  again  seems  to  be 
in  the  formation  of  an  entirely  new  slag  which,  being  clean, 
favours  the  more  rapid  removal  of  the  remaining  silicon, 
phosphorus,  and  carbon.  The  second  part  of  the  operation 
occupies  about  two  and  a  half  hours. 

Remarks. — There  is  little  doubt  but  that  the  rate  of 
manufacture  of  open  hearth  steel  will  continue  to  advance, 
while  that  of  Bessemer  steel  will  probably  decrease,  or  at 
any  rate  will  make  little  or  no  progress.  This  is  largely 
due  to  the  more  regular  quality  of  the  open  hearth  metal 
on  account  of  the  greater  control  that  can  be  exercised  over 
the  process.  Still,  with  the  new  impetus  given  by  the  use 
of  mixers  the  older  process  is  not  likely  to  decline  very 
rapidly.  In  1906,  more  than  12,000,000  tons  of  Bessemer 
ingots  were  cast  in  America,  while  the  output  of  the  open 
hearth  amounted  to  nearly  10,000,000  tons.  It  is  reported, 


THE   OPEN    HEAETH  PEOOESS.  213 

however,  that  eighty-six  new  open  hearth  furnaces  are  in 
course  of  erection  in  different  parts  of  the  United  States. 
The  capacity  of  these  furnaces  will  be  from  50  to  60  tons, 
and  the  estimated  yearly  output  about  4,000,000  tons.  No 
such  increase  is  indicated  in  connection  with  the  Bessemer 
process. 

The  basic  process  is  largely  increasing  in  both  cases,  and 
this  is  due  to  several  causes,  the  principal  one  of  which  is 
the  demand  by  the  acid  process  for  a  high-class  pig  iron 
practically  free  from  phosphorus.  This  demand  is  becoming 
more  difficult  to  meet,  as  non-phosphoric  ores  are  not  nearly 
so  widely  distributed  and  abundant  as  phosphoric  ones. 
Also,  the  natural  prejudice  against  basic  steel  engendered  by 
the  old  practice  of  considering  any  kind  of  scrap  good 
enough  to  convert  into  this  class  of  metal  is  being  gradually 
overcome.  The  only  limit  to  the  scrap  seemed  to  be  the 
width  of  the  furnace  doors ;  but  now,  with  careful  selection 
of  the  materials,  there  is  no  reason  why  the  metal  should  not 
satisfy  every  test  for  purposes  to  which  ingot  metal  can 
be  put.  As  will  be  indicated  in  Chap.  IX.,  much  scrap  is 
necessarily  made  in  working  up  the  ingots,  and  the  open 
hearth  is  hungry  for  it.  It  is  a  case  of  furnace  to  shears, 
and  back  again  to  the  furnace.  But  in  the  Bessemer 
process  the  use  of  scrap  is  very  limited. 

The  higher  carbon  steels  are  more  often  a  product  of 
the  open  hearth  than  of  the  Bessemer  converter.  A  few  of 
the  uses  to  which  open  hearth  steel  is  put  are  indicated 
below  : — 

Boiler  plates    .         .         .       0*20  per  cent.  C. 
Sheets     ....       0*20 
Structural  steel        .         .       0'25          ,, 
Rails        ....       0*45 
Springs   ....       0*65          ,, 
Tools  .       1-30 


CHAPTEE  IX. 

MECHANICAL    TREATMENT    OF    IRON    AND    STEEL. 

IN  the  preceding  chapters  the  production  of  masses  of 
iron  and  steel  in  a  sufficiently  pure  state  to  be  worked 
under  the  hammer  and  between  rolls  has  been  described. 
In  this  chapter  the  physical  and  mechanical  treatment 
necessary  to  render  the  metal  suitable  for  the  use  of  the 
engineer  and  mechanician  generally  will  be  considered. 


THE  IRON  MILL, 

Treatment  of  Blooms. — The  ancient  ironworker  with  his 
small  furnace  would  have  only  small  masses  of  metal  to 

deal  with,  but  they 
would  be  in  a  spongy 
state,  and  wet  with 
fluid  cinder,  so  that 
hammering  to  con- 
solidate  them  and  re- 

FIG.  45.-The  Helve  Hammer.  move  the  cinder  as  far 

as  possible   would  be 

necessary.  The  hand  hammer,  however,  would  be  sufficient 
for  the  purpose.  But  as  the  furnaces  increased  in  size  the 
blooms  from  them  were  larger,  and  the  use  of  sledges  even 
would  be  ineffective,  so  that  where  water  power  was  available, 
power  hammers  would  come  into  use  for  manipulating  these 
larger  pieces  of  metal.  Such  hammers  are  very  simple  in 
principle,  and  are  still  somewhat  extensively  used,  even  when 
steam  has  to  furnish  the  motive  power.  They  are  of  two 


MECHANICAL  TEEATMENT  OF   IEON  AND   STEEL.     215 

kinds,  the  tilt  hammer  and  the  helve  hammer,  and  are  based 
upon  the  lever  principle.  In  the  tilt  form  the  fulcrum  is 
nearer  one  end,  and  the  hammer  head  is  fixed  at  the  end  of 
the  longer  arm.  In  the  helve  hammer  the  lever  is  of  the 
second  order,  with  the  fulcrum  at  one  end  and  the  hammer 


FIG.  46.— Interior  of  the  Clay  Wheel  Forge  showing  Tilt  Hammers 
driven  by  Water  Power. 

head  near  to  the  other.  The  motive  power  is  furnished  by 
a  wheel  with  a  number  of  projections  on  its  rim ;  and  when 
these  projections  are  made  to  press  down  upon  the  end  of 
the  short  arm  of  the  lever  to  raise  the  hammer  it  is  of  the 
tilt  form ;  but  when  the  projections  press  upwards  upon  the 
end  near  the  head  to  raise  it,  it  is  of  the  helve  form. 


216  IEON  AND   STEEL. 

Fig.  45  will  serve  to  illustrate  the  general  principle  of  the 
helve.  If  the  tail  of  the  helve  is  made  to  project  a  little 
beyond  the  fulcrum,  and  the  driving  wheel  is  arranged  for 
its  projections  to  press  down  the  tail  piece  and  then  release 
it,  the  arrangement  is  that  of  a  tilt  hammer. 

Fig.  46  shows  the  interior  of  the  Clay  Wheel  Forge  with 
tilt  hammers  in  position ;  and  Fig.  47  is  a  view  of  the 
exterior  of  the  forge  showing  the  water  wheels  by  which 
the  hammers  are  driven.  The  forge  is  situated  on  the 
river  Don,  about  three  miles  from  Sheffield,  and  is  still 
doing  its  daily  work  under  the  direction  of  Messrs.  Firth. 

The  tilt  hammer  is  used  for  light  work,  and  the  part  to 
be  raised  rarely  exceeds  5  cwts.,  often  much  less.  On  this 
account  it  can  be  driven  rapidly,  and  made  to  deliver  a  large 
number  of  moderate  blows  to  the  piece  of  metal  on  the 
anvil  beneath.  It  is,  no  doubt,  the  original  form  of  the 
power  hammer,  and  is  still  in  use  in  the  small  fineries  of 
Styria  and  Sweden. 

On  the  other  hand,  the  helve  is  used  for  heavy  work,  and 
is  of  considerable  size,  the  part  to  be  raised  often  weighing 
from  8  to  10  tons,  and  having  a  drop  of  two  feet.  It  can  be 
made  to  deliver  its  blows  at  varying  speeds  up  to  sixty  per 
minute.  It  is  still  to  be  seen  doing  excellent  work  in  some 
large  forges,  but  is,  of  course,  driven  by  steam  power. 

Treatment  of  Puddled  Balls. — The  spongy  mass  of  refined 
metal  drawn  from  the  puddling  furnace  at  the  end  of  the 
process  is  at  a  welding  heat,  and  wet  with  molten  cinder. 
It  is  taken  direct  to  the  steam  hammer,  or  other  form  of 
shingling  apparatus,  and  thoroughly  hammered  or  squeezed 
into  a  more  or  less  rectangular  mass.  While  the  hammering 
is  going  on  sparks  fly  in  all  directions,  liquid  cinder  flows 
out,  and  jets  of  burning  gas  spurt  from  the  glowing  mass. 
All  exposed  parts  of  the  body  of  the  hammerman  are  pro- 
tected by  sheet  iron  or  leather,  and  to  the  onlooker  he  has 
a  very  formidable  appearance.  The  work  of  the  hammer- 


MECHANICAL  TREATMENT   OF   IRON   AND   STEEL.     217 


60 
_C 

I 

o> 


218  IRON  AND   STEEL. 

man  is  to  turn  over  the  hot  mass  so  that  it  shall  be 
uniformly  welded  under  the  rapid  blows  of  the  hammer. 
As  the  operation  proceeds  the  metal  settles  down  and  is 
finally  formed  into  a  rough  square  slab  or  bar.  As  the 
mechanical  energy  of  the  -hammer  is  largely  converted  into 
heat  during  the  hammering  it  helps  to  keep  up  the 
temperature  of  the  metal,  and  so  favours  the  expulsion  of 
the  cinder,  which,  however,  is  never  complete.  The 
expelled  cinder,  which  is  a  fairly  pure  form  of  tap  cinder, 
collects  round  the  hammer,  and  is  called  hammer  slag.  It  is 
used,  as  already  described,  as  a  flux  in  the  puddling  process 
itself. 

Steam  hammers  used  for  shingling  are  not  very  large,  as 
the  work  they  have  to  do  is  not  particularly  heavy.  The 
steam  hammer  was  invented  by  Watt  and  improved  by 
Nasmyth,  so  that  it  often  bears  the  latter's  name.  In  its 
perfect  form  it  consists  of  a  steam  cylinder  and  piston 
supported  by  standards.  The  hammer  head  or  "tup"  is 
fixed  to  the  outer  end  of  the  piston  rod  by  a  kind  of  ball- 
and-socket  joint,  which  allows  of  a  little  play,  and  thus 
prevents  the  piston  from  snapping,  as  it  moves  up  and  down 
in  the  guide  grooves  between  the  standards.  The  anvil  block 
upon  which  the  work  is  placed  is  directly  under  the  head. 
The  whole  should  be  fixed  upon  a  very  firm  foundation,  as 
the  vibration  is  very  great  when  the  hammer  is  at  work. 
The  larger  the  hammer  the  greater  the  care  required  in 
making  it  solid.  When  steam  is  admitted  below  the  piston 
the  hammer  is  raised,  and  when  it  is  admitted  above  the 
piston  the  hammer  is  driven  down;  and  the  energy  of  the 
steam  being  added  to  the  energy  of  the  falling  mass 
increases  the  strength  of  the  blow  given  to  a  body  on  the 
anvil.  In  a  "  drop  "  hammer  the  steam  is  admitted  under 
the  piston  only,  and  the  energy  of  the  blow  it  delivers 
entirely  depends  upon  the  weight  of  the  head  and  the 
height  from  which  it  falls.  Also,  the  workman  has  very 


MECHANICAL   TREATMENT   OF   IRON    AND   STEEL.     219 

little  control  over  this  form  of  hammer  ;  but  when  the  piston 
is  double-acting  the  blow  can  be  regulated  with  the  greatest 
precision,  and  very  skilful  work  can  be  done.  The  steam 


FIG.  48. — Steam  Hammer. 

valves  are  connected  by  lever  or  screw  gearing  with  the 
working  handles,  and  the  hammer  may  be  stopped  suddenly 
at  any  part  of  its  journey.  Fig.  48  is  an  illustration  of  a 
modern  hammer. 


220  IRON  AND   STEEL. 

Squeezers. — In  hammering  puddled  balls  the  first  blows 
are  delivered  so  as  to  exert  a  squeezing  action  as  far  as 
possible,  for  it  is  desired  to  extend  the  effects  of  the  blows 
right  to  the  centre  of  the  mass.  Herein  lies  the  principal 
defect  of  all  hammers.  The  blow  is  delivered  rapidly,  and 
its  effect  in  the  case  of  a  large  mass  of  metal  does  not 
extend  to  the  centre;  so  that  the  interior  is  not  properly 
consolidated.  In  some  cases  a  prolonged  pressure,  which 
thus  has  time  to  extend  through  the  whole  mass,  gives  better 
results.  This  led  to  the  introduction  of  squeezers,  for  dealing 
with  the  large  blooms  produced  in  mechanical  furnaces  such 
as  the  Danks  and  the  Siemens  rotators.  In  the  crocodile 
squeezer  the  hot  bloom  is  forced  between  two  heavy  jaws, 
which  are  made  to  open  and  close  by  means  of  a  powerfully 
driven  crank  and  connecting  rod.  The  lower  jaw  is  fixed, 
and  the  upper  one  movable.  The  shingler  is  thus  able  to 
push  in  the  ball  as  the  jaw  rises,  so  that  it  is  gripped  by 
the  serrated  under-surface  of  the  jaw  as  it  descends,  and  is 
effectively  squeezed.  This  is  repeated  until  the  shingling 
is  finished. 

Rotatory  squeezers  are  usually  very  simple  in  principle. 
In  one  form  a  segment  of  a  strong  iron  cylinder  is  fixed  writh 
its  cross-section  horizontal,  and  a  smaller  complete  cylinder 
is  made  to  revolve  eccentrically  within  it  so  that  the  space 
between  the  fixed  and  the  moving  surfaces  gradually 
decreases  in  width.  The  working  surfaces  are  serrated,  so 
that  when  a  bloom  is  pushed  into  the  widest  part  of  the 
space  between  the  fixed  and  moving  parts  it  is  gripped, 
dragged  through  the  gradually  narrowing  space,  and  finally 
expelled  from  the  narrowest  part  thoroughly  squeezed  and 
ready  for  the  rolls.  The  cinder  squeezed  out  drips  through 
the  bottom  of  the  machine. 

In  another  form  of  squeezer  two  rolls  are  made  to  revolve 
on  the  same  level  and  in  the  same  direction  by  means  of 
a  pair  of  horizontal  and  parallel  shafts,  while  a  large  cam 


MECHANICAL  TEEATMENT  OF  IEON  AND   STEEL.     221 

revolves  above  them  in  such  a  way  that  the  space  between 
the  cam  and  the  rolls  gradually  decreases.  The  bloom  is 
dropped  into  this  space  when  it  is  at  its  widest,  and  is  slowly 
squeezed  by  the  combined  motion  of  the  rolls  and  cam. 
At  the  same  time  its  exposed  end  is  hammered  by  a  small 
horizontal  steam  hammer.  The  cinder  drips  out  between 
the  rolls. 

Puddled  Bar. — The  rough  slab  of  metal  when  it  comes 
from  the  hammer  or  other  shingling  apparatus  is  still  at 
a  bright  red  heat,  and  is  taken  straight  to  the  forge-train, 
passed  through  the  rolls,  and  thus  worked  down  to  puddled 
bar.  The  forge  rolls  consist  of  two  pairs,  one  for  roughing 
and  the  other  for  finishing.  The  spaces  between  the 
roughing  rolls  are  diamond-shaped,  and  the  working 
surfaces  in  the  larger  ones  are  roughened  so  as  to  grip  the 
metal  better.  The  spaces  between  the  finishing  rolls  are 
oblong  with  the  long  side  horizontal.  The  rolls  them- 
selves are  usually  made  of  close  grained  cast  iron.  Their 
necks  run  in  gun-metal  bearings  supported  in  heavy  iron 
frames  firmly  bolted  to  the  ground.  The  bottom  rolls  are 
keyed  together,  and  are  driven  by  a  shaft  attached  to  the 
end  of  one  of  the  rolls.  The  top  rolls  are  usually  geared 
to  the  bottom  ones  so  that  they  revolve  with  them  but  in 
the  opposite  direction,  and  the  distance  between  them  is 
regulated  by  screws  that  pass  through  the  tops  of  the 
"housings"  to  the  upper  bearings.  The  usual  rate  of 
revolution  is  from  60  to  80  per  minute. 

The  hot  slab  is  passed  through  the  largest  space  in  the 
roughing  rolls,  sent  back  over  the  top  roll,  passed  through 
the  next  largest  space,  and  so  on  to  the  end  of  the  finishing 
rolls,  from  which  a  somewhat  rough  rectangular  bar — the 
puddled  bar — is  obtained,  the  original  heat  of  the  metal 
allowing  this  much  work  to  be  put  upon  it. 

Merchant  Bar. — The  bars  produced  as  described  above 
are  very  rough-looking  and  far  from  homogeneous  in 


222  IKON  AND   STEEL. 

structure,  as  they  still  contain  cinder  distributed  through 
their  mass  in  more  or  less  irregular  patches.  These  bars 
are  sent  to  the  mill  to  be  cut  up  into  short  lengths  and  made 
into  piles.  The  piles  are  then  raised  to  a  welding  heat  and 
worked  down  to  the  required  sections.  A  stand  of  rolls  is 
shown  in  Fig.  49. 

The  Reheating  or  Mill  Furnace  in  which  these  piles   are 
heated  is  of  the  reverberatory  type,  and  is  fired  either  by 


FIG.  49.— Eolls. 

solid  or  gaseous  fuel.  A  vertical  section  through  a  coal- 
fired  furnace  is  shown  in  Fig.  50,  which  will  serve  to 
illustrate  the  construction  and  use  of  such  furnaces.  It  is 
similar  in  general  form  to  the  puddling  furnace,  but  the 
ratio  between  the  grate  and  the  bed  is  not  quite  so  large. 
The  working  bottom  is  usually  lined  with  sand,  and  slopes 
from  the  fire  bridge  to  the  flue,  while  the  roof  slopes  in  the 
same  direction  as  the  bed.  The  bed  plates  are  of  iron,  and 
the  inner  structure  is  of  firebrick,  cased  on  the  outside 
with  iron  plates.  There  is  one  door,  sometimes  two,  on  the 
working  side,  and  the  usual  firing  hole.  In  some  furnaces 
a  layer  of  oxide  of  iron  is  used  for  a  working  bottom,  and 
in  others  the  sand  is  replaced  by  basic  slag. 

The  temperature  of  the  furnace  has  to  be  kept  up  to  a 
welding  heat.     The  piles  are  carefully  placed  lengthwise 


MECHANICAL  TREATMENT  OF  IRON  AND  STEEL.    223 

across  the  bed  by  means  of  a  charging  tool  called  the 
"  peel,"  and  when  the  full  charge,  from  one  to  two  tons,  has 
been  put  in  the  door  is  closed,  and  the  air  excluded  as  much 
as  possible.  The  fire  is  made  up,  and  the  piles  are  turned 
occasionally  so  that  they  may  be  uniformly  heated.  The 
reheating  takes  from  fifteen  minutes  to  an  hour  according 
to  the  weight  of  the  piles,  which  varies  from  \  cwt.  to  6  cwts., 


FIG.  50. — Reheating  or  Mill  Furnace. 
A,  Bed;  B,  Working  door;   (7,  Firing  door;  7),  Grate;  E,  Chimney. 

according  to  the  size  of  the  section  to  be  produced.  The 
pile  when  hot  enough  is  withdrawn  by  means  of  a  pair  of 
tongs,  transferred  to  a  small  iron  trolley,  and  at  once  taken 
to  the  rolls.  When  the  furnace  has  been  discharged  the 
bottom  is  made  up  and  a  fresh  charge  introduced.  The 
cinder  drains  down  the  slope  of  the  bed  and  runs  from 
the  flue  end.  It  is  known  as  "  mill  cinder  "  or  "  flue 
cinder,"  and  consists  largely  of  ferrous  silicate  rich  in  silica 
when  a  sand  bottom  is  used.  When  an  "  oxide  "  bottom 


224  IEON  AND   STEEL. 

is  used  the  cinder  is  much  richer  in  oxides  of  iron,  and  is 
more  valuable. 

A  coal-fired  furnace  is  comparatively  inexpensive  to  build 
and  is  easily  worked,  but  these  are  its  only  recommenda- 
tions, for  it  is  very  extravagant  in  fuel,  using  from  three  to 
four  times  as  much  as  a  gas-fired  furnace  to  do  the  same 
amount  of  work.  The  latter  form  of  furnace  is,  therefore, 
very  largely  used. 

The  changes  taking  place  in  the  reheating  process  are 
simple  in  character,  for  if  air  is  excluded  from  the  furnace 
as  much  as  possible  the  amount  of  oxidation  should  not  be 
serious.  As  the  temperature  of  the  pile  increases  the 
cinder  mechanically  mixed  with  the  metal  in  the  bars 
liquefies,  and  part  of  it  liquates  out.  In  doing  so  it  is 
brought  into  contact  with  the  small  quantity  of  impurities 
not  removed  in  the  puddling  process,  and  being  oxidising 
in  character,  oxidises  and  carries  them  out.  In  this  way, 
not  only  is  the  quantity  of  intermixed  slag  reduced,  but 
also  small  quantities  of  phosphorus,  carbon,  and  sulphur 
are  removed.  This  liquated  cinder,  together  with  that 
formed  by  the  oxidation  of  the  metal  itself,  makes  up  the 
flue  cinder  which  runs  from  the  furnace.  The  process  is, 
therefore,  to  some  extent,  a  refining  as  well  as  a  reheating 
one. 

The  reheated  pile  is  taken  to  the  rolls,  and  rolled  down 
into  a  bar,  sheet,  or  section  as  required.  A  further  improve- 
ment in  the  structure  and  quality  of  the  metal  is  sometimes 
effected  by  cutting  up  the  bars,  piling,  and  reheating  them 
a  second,  or  even  a  third  time.  This  extra  work,  however, 
increases  the  price  as  well  as  the  quality  of  the  metal.  But 
the  best  qualities  of  bar  iron  are  now  produced  more  by  the 
careful  selection  of  the  materials  and  their  systematic  treat- 
ment during  the  manufacture. 

The  rolls  used  in  the  production  of  the  various  forms  of 
merchant  iron  vary  much  in  shape  according  to  the  sections 


MECHANICAL  TKEATMENT   OF   IRON  AND   STEEL.     225 

to  be  produced.  Roughing  rolls  and  finishing  rolls  that 
have  to  be  turned  to  shape  are  cast  in  sand  from  a  good 
mixture  of  foundry  irons,  or  from  mild  steel.  Sometimes 
they  are  made  of  forged  steel,  and  although  the  first  cost 
is  greater  the  rolls  are  much  more  durable.  Eolls  are  also 
cast  in  a  heavy  iron  mould  by  which  the  metal  is  chilled 
to  a  depth  of  from  J  inch  to  f  inch,  and  a  shell  of  hard 
white  iron  thus  formed.  Such  rolls  are  used  for  finishing 
sheets  and  plates  that  are  intended  to  have  a  smooth 
surface.  The  rolls  in  an  iron  mill  generally  vary  from 
6  inches  to  18  inches  in  diameter. 

The  mill  train,  like  the  forge  train,  usually  consists  of 
two  sets  of  rolls,  one  for  roughing  and  one  for  finishing, 
and  resembles  it  generally.  The  bottom  finishing  roll, 
especially  for  small  sections,  has  a  stripping  plate  in  front 
of  it  that  follows  the  contour  of  the  roll  to  direct  the  section 
outwards,  and  so  prevent  it  from  wrapping  round  the  roll. 
For  some  purposes,  such  as  sheet  rolling,  the  distance 
between  the  rolls  must  be  readily  and  accurately  adjustable. 
They  are,  therefore,  fitted  with  adjusting  screws  that  can 
be  turned  by  lever  arms  within  reach  of  the  roller.  The 
bottom  roll  is  always  made  a  little  smaller  than  the  top  one, 
which  tends  to  make  the  section  bend  downwards  as  it 
passes  through,  and  thus  prevents  it  from  wrapping  round 
the  top  roll. 

For  rolling  small  light  sections  guide  mills  are  used  in 
which  the  bars  are  directed  into  the  passes  between  the 
rolls  by  guide  plates  fixed  opposite  the  collars  on  each  side 
of  the  pass.  This  is  necessary  because  the  work  has  to  be 
done  rapidly,  as  such  thin  sections  cool  quickly.  A  fuller 
description  of  the  apparatus  and  processes  will  be  found  in 
the  section  on  Steel  Mills. 

In  the  manufacture  of  sections  such  as  angle,  tee,  and 
channel  iron,  wrought  iron  is  being  replaced  by  mild  steel, 
and  for  unmarked  bar,  for  which  there  is  no  guarantee  of 

i.s.  Q 


226  IEON  AND  STEEL. 

quality,  the  competition  is  so  keen  that  it  scarcely  pays  to 
make  it.  But  marked  bars  of  good  quality  will  hold  their 
own,  as  the  metal  undoubtedly  works  better  in  the  smithy 
than  mild  steel.  Best  Yorkshire  bar  iron  has  already  been 
noticed  for  its  quality. 

THE  STEEL  MILL. 

In  considering  the  mechanical  processes  for  the  treatment 
of  steel,  it  must  be  borne  in  mind  that  the  metal  comes 
from  the  furnace  in  the  fluid  state  and  is  cast  into  ingots  ;  so 
that  it  is  in  a  different  condition  to  the  puddled  iron  already 
considered.  With  iron  the  welding  process  may  be  carried 
out  to  any  extent  within  the  limits  of  the  apparatus  at  hand, 
and  large  masses  may  be  built  up  by  welding  smaller  ones 
together,  for  the  metal  can  be  raised  to  a  welding  heat  and 
welded  perfectly  under  the  hammer  without  serious 
deterioration.  But  small  steel  ingots  cannot  be  welded 
together  to  form  larger  masses  in  the  same  way,  so  that 
whatever  may  be  the  size  of  the  section  required  the  metal 
to  form  it  must  be  cast  into  one  ingot. 

In  the  old  puddling  days  large  masses  of  metal  were 
seldom  treated;  and  the  iron  mill  was  furnished  with  com- 
paratively small  and  simple  apparatus;  nor  was  there  any 
difficulty  in  dealing  with  the  waste,  as  the  crop  ends  could 
be  included  in  the  piles  for  reheating,  and  so  used  up.  But 
had  it  not  been  for  the  introduction  of  the  Bessemer  and 
open  hearth  processes,  further  development  would  no  doubt 
have  taken  place,  for  the  mechanical  puddling  furnaces 
described  at  the  end  of  Chapter  Y.  would  have  been  improved 
and  enlarged.  The  men,  however,  who  could  have  done 
this  had  their  energies  diverted  into  other  channels  during 
the  development  of  the  new  processes. 

Treatment  of  Ingot  Metal. — Now  when  a  piece  of  iron  or 
steel  is  heated  it  expands  and  increases  in  volume  as  the 


MECHANICAL  TREATMENT  OF  IRON  AND   STEEL.     227 


temperature  rises.  When  it  liquefies  there  is  a  further 
expansion,  for  the  liquid  occupies  a  larger  volume  than  the 
solid  at  the  same  temperature,  and  the  higher  the  tempera- 
ture is  above  the  melting  point  the  larger  will  the  volume 
be.  Exactly  the  reverse  changes  take  place  as  the  liquid 
cools,  freezes,  and  then  cools  to  the  temperature  of  the  air. 
If,  then,  a  given  volume  of  molten  steel  is  run  from  a  ladle 
into  a  mould,  the  volume  of  the  ingot  into  which  it  solidifies 
will  be  considerably  smaller  than  the  original  volume.  The 
amount  of  this  contraction  is,  roughly,  6  per  cent,  of  the 
original  volume.  If  the  mass  could  by  any  means 
be  made  to  solidify  uniformly  from  its  centre, 
the  ingot  would  occupy  a  smaller  volume  than 
the  fluid  metal,  and  be  uniform  in  structure. 
But  exactly  the  reverse  takes  place,  for  the 
metal  in  contact  with  the  cold  surface  of  the 
mould  is  at  once  chilled  and  solidified  with 
formation  of  a  thin  shell.  This  shell  thickens 
as  the  metal  cools,  and  as  it  contracts  during 
the  solidification,  the  fluid  metal  in  the  interior 
is  left  in  a  larger  cavity,  so  that  it  sinks.  But 
as  a  skin  has  also  formed  on  the  free  surface 
in  contact  with  the  air,  it  falls  in  a  little  as  the 
fluid  sinks  from  under  it  to  form  the  well-known  cavity  or 
"  pipe  "  usually  found  in  the  top  of  the  solid  ingot  (see 
Fig.  51).  The  metal  crystallises  as  it  solidifies,  and  in  doing 
so  passes  through  a  pasty  state.  When  the  central  portion 
is  just  about  to  set  it  is  in  this  condition,  and  is  surrounded 
by  a  thick  shell  which  it  is  trying  to  fill.  If  it  succeeds 
the  solid  will  be  spongy,  but  if  not,  a  crack  or  cracks  will 
develop  in  it.  This  is  a  defect  in  the  ingot,  as  the  sides  of 
the  crack  do  not  weld  together  under  further  treatment. 
Cracks  due  to  contraction  are  of  the  same  nature  as 
the  pipe.  Now  if  the  metal  were  pure,  and  no  cracks 
developed,  the  pipe  would  form,  and  the  mass  generally 

Q2 


FIG.  51. 


228  IRON  AND   STEEL. 

would  be  in  a  state  of  unequal  strain  with  a  tendency  to 
sponginess. 

Segregation. — But  when  the  metal  is  impure,  as  is  usually 
the  case,  the  impurities,  such  as  phosphorus,  sulphur, 
carbon,  etc.,  are  combined  with  a  portion  of  the  iron,  and 
these  compounds  have  a  lower  melting  point  than  the  main 
mass.  As  the  solidification  proceeds  from  the  outside  these 
fluid  bodies  are  partially  squeezed  inwards  from  layer  to 
layer  towards  the  centre,  and  generally  towards  the  top  of 
the  ingot.  The  movement  of  the  impurities  inwards  is 
known  as  segregation.  This  action  is  more  often  beneficial 
than  otherwise,  as  it  tends  to  concentrate  the  impurities  in 
one  part  of  the  mass.  With  a  moderate  percentage  of 
impurities  present  the  segregation  is  fairly  uniform,  as  is 
shown  by  analyses  of  different  parts  of  the  ingot,  and  by 
practical  experience ;  but  when  the  metal  is  very  impure 
the  segregation  is  not,  as  a  rule,  uniform. 

Occlusion  of  Gases.  —  Liquids  dissolve  gases,  and  the 
volumes  of  different  gases  dissolved  by  a  given  liquid  depends 
upon  the  nature  and  volume  of  the  liquid,  the  nature  of  the 
gas,  and  the  temperature  and  pressure  at  which  the  dissolu- 
tion is  effected.  The  effect  of  pressure  is  indicated  by  the 
rush  of  gas  from  the  -liquid  in  a  soda  water  syphon  when 
the  pressure  is  suddenly  reduced  by  opening  the  valve. 
Also,  when  a  liquid  solidifies  on  cooling,  gas  dissolved  in  it 
is  largely  liberated  as  such.  This  is  noticed  in  the  case  of 
water,  which  always  contains  a  small  quantity  of  dissolved 
air,  for  when  it  freezes  the  dissolved  gas  is  liberated  and  then 
imprisoned  in  the  form  of  bubbles  in  the  solid  mass.  This  is 
due  to  the  water  solidifying  first  on  the  surface  and  forming 
a  crust  of  ice  which  prevents  the  expelled  gas  from  escap- 
ing. All  gas  not  expelled  during  solidification  is  left  in 
solid  solution. 

Now  when  a  metal  absorbs  a  gas  and  retains  it  after 
solidification  the  gas  is  said  to  be  occluded  by  the  metal ; 


MECHANICAL  TREATMENT   OF  IBON  AND   STEEL.     229 

but  the  absorption  may  take  place  when  the  metal  is  in  the 
solid  or  semi-solid  condition,  as  in  the  absorption  of  carbon 
monoxide  by  red  hot  iron,  which  was  proved  by  Graham. 
Hydrogen  and  nitrogen  are  dissolved  by  iron,  and  when 
both  are  present  they  may  be,  in  part  at  least,  in  combina- 
tion with  each  other  as  ammonia.  Gaseous  hydrocarbons 
may  also  be  present,  and  some  authorities  say  carbon 
dioxide  too ;  but  this  is  somewhat  difficult  to  account  for, 
as  carbon  dioxide  is  reduced  to  the  monoxide  by  red  hot 
iron. 

The  method  of  detecting  the  presence  of  gas  bubbles  in 
the  solid  metal  is  to  drill  a  piece  of  it,  either  under  water  or 
under  mercury,  in  such  a  way  that  the  escaping  gas  can  be 
collected,  measured,  and  analysed.  The  problem  is  a 
difficult  one,  and  varying  results  have  been  obtained  by 
different  observers ;  but  that  does  not  affect  the  general 
statement  that  gas  does  remain  in  solid  solution  in  iron 
and  steel  at  ordinary  temperatures.  The  influence  of 
occluded  gas  on  the  physical  and  mechanical  properties  of 
the  metal  is  not  at  all  understood,  but  there  seems  to  be  a 
general  consensus  of  opinion  that  if  the  gas,  whatever  may 
be  its  nature,  can  be  kept  in  solid  solution,  its  influence 
may  be  neglected.  It  is  when  the  gas  is  liberated  in  the 
pasty  metal  and,  failing  to  escape,  causes  blow-holes,  that 
difficulties  arise. 

A  mass  of  molten  steel  may  be  fairly  tranquil  in  the  ladle 
and  still  contain  a  considerable  volume  of  gas  in  solution, 
but  when  it  is  teemed  into  the  mould  the  gas  commences  to 
escape,  and  this  escaping  gas  usually  consists  of  hydrogen, 
nitrogen  and  carbon  monoxide  during  a  normal  solidification. 
But  sometimes,  when  the  deoxidisers  have  not  removed  the 
oxygen  sufficiently,  reaction  takes  place  between  it  and 
carbon,  with  formation  of  carbon  monoxide  and  dioxide, 
and  the  sudden  escape  of  these  gases  will  sometimes  cause 
the  metal  to  boil  out  of  the  centre  of  the  ingot,  and  leave 


230  IEON  AND  STEEL. 

only  a  shell  in  the  mould.  This  phenomenon  is  known  as 
a  "  wild  heat,"  and  the  metal  is  said  to  be  "  wild."  It  is 
well  known  that  certain  chemical  changes  are  held  in 
abeyance  until  the  temperature  falls  below  a  certain  limit, 
and  then  take  place  rapidly.  This  is  the  probable  reason 
why  the  metal  does  not  "  boil  "  until  it  is  in  the  mould. 
This  wildness  is  usually  noticed  in  the  case  of  Bessemer 
metal  that  has  blown  too  hot  from  the  presence  of  too  much 
silicon  in  the  charge.  The  deoxidisers  are  then  not  able  to 
sufficiently  reduce  the  oxide  of  iron  formed,  and  the  metal 
is  "wild." 

The  presence  of  a  dissolved  solid  in  the  solution  of  a  gas 
may  prevent  the  liberation  of  the  gas,  while  the  solution 
itself  becomes  solid,  and  this  is  put  into  practical  use  for 
the  prevention  of  blow-holes  in  ingots.  Aluminium  and 
silicon  seem  to  possess  this  property,  though  why  the  gases 
are  kept  in  solid  solution  by  these  elements  is  not  clear, 
but  the  actual  result  is  remarkable.  The  writer  saw  an 
experiment  to  demonstrate  this  conducted  in  Prof.  Arnold's 
laboratory  at  Sheffield.  Two  exactly  similar  charges  were 
melted  down  in  two  crucibles  placed  side  by  side  in  the 
same  fire ;  after  they  had  been  molten  for  some  time  a 
small  piece  of  aluminium  was  dropped  into  one  of  the 
crucibles,  and  both  charges  were  teemed  into  similar 
moulds.  The  ingot  containing  the  aluminium  was  very 
compact  and  considerably  shorter  than  the  other,  which, 
from  its  appearance,  was  very  spongy  towards  the  top.  On 
the  same  day  he  saw  a  few  ounces  of  aluminium  thrown 
into  a  ladle  containing  20  tons  of  steel  ready  for  casting. 
Aluminium  and  silicon  may  also  act  as  deoxidisers,  and 
thus  prevent  carbon  from  reducing  oxide  of  iron,  left  in  by 
the  manganese,  with  liberation  of  carbon  monoxide. 

It  would  appear,  however,  that  ferro-aluminium  is  the 
best  form  in  which  to  introduce  the  aluminium  on  the  large 
scale.  Ferro-silicon  is  used  in  the  same  way,  and  Pourcel, 


MECHANICAL  TREATMENT  OP   IRON  AND   STEEL.     231 

the  French  metallurgist,  states  that  he  always  found  silicon 
in  steel  free  from  blow-holes,  which  supports  the  statement 
that  the  silicon  acts  by  keeping  the  gases  in  solution. 

The  escape  of  gases  from  the  molten  metal  is  facilitated 
by  rapidly  rotating  a  paddle  in  it  just  before  tapping  it  from 
the  ladle  into  the  moulds.  This  purely  mechanical  process 
was  introduced  by  Mr.  Allen. 

The  influence  of  pressure  in  keeping  the  gases  in  solution 
has  been  practised,  and  this  pressure  has  been  applied  in  a 
variety  of  ways.  At  the  Krupp  works  a  gas-tight  cap  was 
fitted  on  the  top  of  the  mould  into  which  the  metal  had  just 
been  tapped,  and  liquid  carbon  dioxide  was  allowed  to 
vaporise  from  a  strong  receiver  into  the  space  above  the 
molten  metal,  there  to  exert  its  pressure.  Jones,  of 
Pittsburg,  tried  the  effect  of  introducing  high  pressure 
steam  into  a  similar  cap.  But  these  methods,  although 
partially  successful,  have  not  come  into  permanent  use. 

The  Whitworth  Press. — The  method  introduced  by  Sir 
J.  Whitworth  for  compressing  fluid  steel  is  the  most 
successful,  but  as  the  apparatus  is  very  costly  it  has  only 
come  into  limited  use  in  the  casting  of  steel  required  for 
ordnance  purposes.  The  latest  hydraulic  press  used  for 
the  process  can  exert  a  pressure  of  8,000  tons,  and  is 
probably  the  most  powerful  in  existence. 

In  the  Whitworth  process  a  special  mould  able  to  resist  a 
very  powerful  side  thrust  is  required.  It  is  made  up  of  a 
number  of  forged  steel  hoops  lined  with  shaped  cast  iron 
bars.  Kadial  grooves  in  these  bars  open  into  vertical 
channels  between  the  lining  and  rings,  made  by  bevelling 
off  the  outer  edges  of  the  bars.  Gases  have  thus  a  free  exit 
from  the  interior  of  the  mould,  and  can  escape  through  the 
vertical  channels  from  the  top  and  bottom  of  the  mould. 
The  iron  lining  is  coated  internally  with  refractory  material 
spread  on  in  a  layer  about  f  inch  thick.  The  bottom  of  the 
mould  consists  of  an  iron  plate  faced  with  firebrick,  and  the 


232  IEON  AND   STEEL. 

top  is  closed  by  an  iron  plate  with  a  circular  hole  in  it.  A 
plug  faced  with  firebrick  and  fitted  to  the  upper  fixed  table  of 
the  press  can  just  pass  into  the  hole  in  the  top  plate  with  a 
clearance  of  about  ^  inch.  After  the  inside  has  been  coated 
with  plumbago  and  warmed  to  expel  any  moisture,  the  mould 
is  put  into  position  on  a  small  truck  in  the  casting  pit  close 
to  the  press,  and  filled  with  molten  steel :  it  is  then  run, 
with  the  truck,  on  to  the  lower  table  of  the  press.  The  ram 
then  raises  the  table  until  the  plug  enters  the  hole  in  the 
top  plate  of  the  mould.  As  the  ram  moves  upwards  some 
of  the  liquid  metal,  which  is  now  in  contact  with  the  lower 
face  of  the  plug,  is  forced  into  the  annular  space  around  it, 
and,  chilling,  forms  a  perfectly  tight  joint.  As  the  pressure 
is  increased  much  combustible  gas  issues  from  the  top  and 
bottom  of  the  mould  with  a  loud  hissing  noise,  and  burns 
there.  The  gas  is  usually  accompanied  by  a  fine  metallic 
rain.  The  ingot  shortens  rapidly  at  first,  then  slowly,  and 
the  pressure  is  continued  for  a  time  after  the  metal  has  set. 
When  the  mould  has  been  removed  the  ingot  is  found  to 
have  decreased  in  length  by  about  1J  inches  per  foot,  and 
the  proportion  of  scrap  made  in  working  it  is  considerably 
reduced. 

Various  estimates  of  the  pressure  required  to  be  effective 
have  been  given,  and  it  appears  that  any  pressure  under 
2  tons  per  square  inch  is  insufficient.  Sir  J.  Whitworth 
himself  contemplated  using  a  pressure  of  20  tons  per 
square  inch. 

M.  Harmet,  of  St.  Etienne,  France,  uses  a  mould  with  a 
short  square  section  at  the  bottom  and  then  tapered  off  slightly 
to  the  top.  The  top  of  the  mould  is  open,  and  a  cast  iron 
plug  fits  into  the  bottom.  If,  when  the  metal  has  been 
tapped  into  this  mould  and  is  partly  set,  the  plug  is  forced 
upwards  by  a  hydraulic  ram,  the  ingot  is  compressed 
laterally  by  being  driven  up  the  tapering  portion  of  the 
mould.  Harmet  claims  that  the  proportion  of  sound  metal 


MECHANICAL  TREATMENT  OF  IKON  AND   STEEL.     233 

is  considerably  increased.  The  process  has  also  been 
introduced  into  a  Scotch  steelworks. 

The  general  effect  of  pressure  on  the  fluid  appears  to  be  to 
increase  the  proportion  of  sound  metal  in  the  ingots.  But 
although  the  gas  seems  to  be  driven  out,  it  is  the  opinion 
of  those  who  have  had  most  to  do  with  the  process  that  no 
more  gas  is  expelled  than  would  escape  under  normal 
conditions  of  cooling.  Any  blowholes  formed  in  the  pasty 
metal  would,  however,  be  smaller  in  proportion  to  the 
initial  pressure  on  the  gas  in  them  ;  and  it  would  seem  that 
the  general  tendency  would  be  to  keep  such  gas  in  solid 
solution. 

With  regard  to  the  decrease  in  the  weight  of  the 
crop  ends,  this  seems  of  no  importance  in  a  general  way,  as 
the  open  hearth  is  eager  to  take  back  such  waste  metal, 
and,  in  fact,  could  use  up  more  than  is  formed.  It  would 
appear  from  statistics  of  American  practice  that  the  portion 
of  steel  ingots  going  back  to  the  furnace  is  upwards  of 
20  per  cent,  of  the  output.  In  fact,  it  is  only  in  special 
cases  that  ingots  are  treated  in  the  moulds,  except  being 
stoppered  as  in  the  case  of  mild  Bessemer  metal. 

Soaking  Pits. — After  the  mould  has  been  removed  from 
an  ordinary  cast  the  ingot  stands  at  a  red  heat,  and  to  all 
appearance  solid ;  but  as  already  indicated,  the  central 
portion  is  still  fluid,  and  if  it  is  allowed  to  solidify  by 
normal  cooling  in  the  air  the  segregation  will  not  be  so 
perfect  nor  the  strains  in  the  mass  so  uniform  as  if  it  had 
solidified  in  a  hot  shell.  Bessemer  himself  had  this  in 
mind  when  he  covered  the  stripped  ingots  with  sand  to 
retard  the  cooling  ;  but  Gjers  clearly  grasped  the  best  con- 
ditions when  he  introduced  the  principle  of  the  soaking  pit. 
Now  the  shell  is  thick  enough  while  still  at  good  red  heat 
to  allow  of  the  ingot  being  handled.  If  then  it  is  lowered 
into  a  rectangular  chamber,  the  walls  of  which  are  as  hot 
as  the  outside  of  the  ingot,  the  latent  heat  of  liquefaction  of 


234  IEON  AND   STEEL. 

the  solidifying  core  will,  as  it  escapes  outwards,  be  in  part 
arrested  by  the  cooler  shell,  and  the  general  temperature  of 
the  ingot  will  be  increased.  In  this  case,  when  the  whole 
is  solid  it  will  be  hotter  than  the  shell  was  when  the  ingot 
was  put  into  the  chamber.  Also,  the  solidification  will  be 
slower,  and  there  will  be  more  opportunity  for  segregation 
towards  the  top,  and  for  the  equalisation  of  strains  through 
the  mass.  This  is  assisted  by  the  upright  position  of  the 
ingot.  Another  good  point  is  that  the  interior  is  usually 
hotter  than  the  exterior,  and  the  ingot  works  without  a 
"  bone  "  in  it  as  is  sometimes  the  case  with  re-heated 
ingots,  the  outside  of  which  may  be  hotter  and  softer  than 
the  insides.  Theoretically,  the  simple  principle  of  the 
soaking  pit  is  ideal ;  but  it  requires  the  walls  to  be  heated 
first  to  the  necessary  temperature,  and  then  a  constant  and 
regular  supply  of  ingots  to  pass  through  it,  each  ingot  being 
in  the  pit  about  twenty  minutes.  Practically,  these  con- 
ditions are  more  or  less  difficult  to  comply  with,  and  it  is 
usual  to  keep  up  the  temperature  of  the  walls  during  inter- 
mittent supply  by  the  use  of  solid  or  gaseous  fuel  in  modified 
pits.  The  pits  are  generally  built  below  the  floor  level 
close  to  the  mill,  and  have  flues  in  their  side  walls  in  which 
producer  gas  is  burnt,  or,  failing  this,  the  gases  from  a 
slack-fired  grate  attached.  The  pits  can  thus  be  heated 
up  to  commence  work,  and  the  temperature  regulated  during 
working. 

A  Reheating  Furnace,  in  which  the  ingots  can  be  placed 
in  a  vertical  position,  consists  of  a  rectangular  chamber 
lined  with  ordinary  firebricks,  and  divided  at  the  top  by 
brickwork  partitions  that  extend  down  to  about  half  the 
depth  of  the  chamber.  The  spaces  on  the  floor  level 
between  these  partitions  are  fitted  with  covers,  any  one  of 
which  can  be  removed  separately  when  an  ingot  is  to  be 
put  in  or  taken  out.  The  bottom  on  which  the  ingots  rest 
is  best  made  up  of  hard,  infusible  basic  material,  such  as 


MECHANICAL  TEEATMENT   OF  IRON  AND   STEEL.     235 

good  haematite  ore,  hammer  scale,  or  non-siliceous  flue 
cinder.  Messrs.  Harbord  and  Tucker  introduced  the  use  of 
basic  slag  for  this  purpose  some  years  ago,  and  it  has  been 
very  successful.  With  such  a  bottom  very  little  fluid  cinder 
is  formed  in  working,  and  the  little  that  does  form  runs 
away  through  a  tap  hole  provided  for  the  purpose.  For  a 
coal-fired  furnace  the  grate  is  at  one  end  of  the  chamber, 
and  the  products  of  combustion  from  it  pass  through  the 
space  below  the  partitions  to  the  flue,  and  so  keep  up  the 
temperature  of  the  side  walls  and  partitions.  It  is  clear 


FIG.  52. — Gas-fired  Ke-heating  Furnace  or  Soaking  Pits. 

A,  Air  regenerator.  (7,  Working  bottom. 

B,  Gas  regenerator.  D,  Lever  cover  lifter. 

that  such  an  arrangement  can  be  used  to  soak  ingots  as 
well  as  for  reheating. 

Gas-fired  furnaces  to  which  the  regenerative  principle  is 
applied  are  also  used,  especially  in  America.  They  are 
constructed  on  the  same  general  plan  as  the  Siemens  open 
hearth  furnace,  but  the  heating  chamber  is  modified  so  as 
to  receive  the  ingots  in  the  vertical  position,  and  to  allow 
of  working  from  the  floor  level.  Fig.  52  is  an  illustration 
of  a  gas-fired  reheating  furnace  or  soaking  pits.  When  an 
ingot  is  to  be  put  in  one  of  the  spaces  the  cover  is 
removed,  either  by  hooking  it  on  to  a  chain  suspended  from 
a  travelling  crane,  or  by  means  of  a  bent  lever  bar,  the 


236  IEON  AND   STEEL. 

short  arm  of  which  is  pivoted  to  the  axle  of  a  pair  of  wheels, 
so  that  its  end  can  be  pushed  into  a  lug  on  the  cover.  On 
depressing  the  long  arm  of  the  lever  the  cover  is  raised, 
and  can  be  run  back  clear  of  the  opening.  Then  the  ingot, 
suspended  from  the  end  of  a  crane,  and  held  by  a  pair  of 
"  dogs,"  is  brought  over,  lowered  into  the  furnace,  and  the 
cover  replaced.  When  ready  for  the  mill  it  is  taken  out  in 
a  similar  manner. 

To  put  a  partly  solidified  ingot  on  its  side  in  a  reheating 
furnace  is  not  good  practice,  and  should  be  avoided,  for  the 
pipe  at  the  top  of  the  ingot  is  thus  encouraged  to  extend 
itself,  and  in  some  cases  may  run  nearly  the  whole  length 
of  the  ingot.  Another  objection  with  large  ingots, 
which  are  difficult  to  turn  over,  is  that  they  are  not 
uniformly  heated,  so  that  even  with  cold  ingots  it  is  better 
that  they  should  be  re-heated  in  a  vertical  position.  Another 
point  of  importance  in  the  case  of  large  ingots  that  have 
been  allowed  to  get  cold,  is  that  they  should  be  heated  up 
slowly.  Such  ingots  are  in  a  state  of  unequal  strain,  and  if 
put  suddenly  into  a  very  hot  space  may  develop  cracks. 
Also,  steel  ingots  containing  a  high  percentage  of  carbon  must 
be  slowly  and  uniformly  heated,  or  they  will  deteriorate. 
It  is  too  costly  "to  put  such  ingots  into  a  comparatively 
cold  furnace  and  then  gradually  heat  them  up,  for  the  furnace 
would  have  to  be  cooled  down  after  each  heat  before  another 
could  be  charged.  The  difficulty  has  been  got  over  by 
the  use  of  a  furnace  with  a  long  sloping  bed,  into  which  the 
ingots  are  introduced  at  the  flue  end,  and  gradually  rolled 
down  the  bed  into  hotter  and  hotter  positions.  The  ingots 
are  turned  over  and  moved  forwards  by  means  of  iron  bars 
put  through  the  working  doors  in  the  side  of  the  furnace, 
so  that  they  are  heated  uniformly  all  over,  and  ready  to 
withdraw  by  the  time  they  reached  the  fire  bridge.  The  hot 
gases  from  the  grate  in  their  passage  to  the  flue  come  into 
contact  with  cooler  and  cooler  ingots,  by  which  their  heat 


MECHANICAL  TREATMENT   OF   IRON  AND   STEEL.     237 

is  absorbed,  and  pass  into  the  flue  at  a  comparatively  low 
temperature.  A  considerable  economy  of  fuel  is  thus 
effected.  The  first  furnace  of  this  description  was  con- 
structed by  Ekman  in  Sweden  about  1848.  Several  modifi- 
cations of  it  have  been  constructed  and  used  in  this  country, 
on  the  Continent,  and  in  America.  One  of  the  latest  is  the 
Talbot  Continuous  Furnace,  which  is  gas  fired  with  pro- 
ducer gas  burnt  in  hot  air.  The  direction  of  the  gas  is  not 
reversed  in  the  furnace,  but  only  in  the  regenerators,  so  that 
one  end  of  the  bed  is  continually  cooler  than  the  other.  The 
bed  slopes  but  slightly,  and  the  ingots,  which  are  put  into 
the  furnace  at  the  cool  end,  are  pushed  along  by  a  hydraulic 
pusher,  and  finally  discharged  on  to  live  rollers,  by  which  they 
are  hurried  off  to  the  mill.  Blooms,  billets,  and  slabs  can 
also  be  reheated  in  continuous  furnaces.  But  they  are  more 
commonly  dealt  with  in  the  ordinary  reheating  furnace. 

The  Rolling  Mill. — The  rolls  used  in  a  steel  mill  are  for 
the  most  part  cast  iron,  and  are  made  from  a  mixture  of 
cold  blast  foundry  irons  of  the  higher  numbers.  For 
chilled  rolls  the  silicon  should  not  be  more  than  1  per  cent, 
and  the  phosphorus  less  than  0*5  per  cent.,  while  the 
sulphur  should  be  less  than  O'l  per  cent.  The  mixture  is 
melted  for  casting  in  a  reverberatory  furnace  fired  with 
coal  low  in  sulphur.  Steel  rolls,  both  cast  and  forged,  are 
also  used,  and  pay  for  the  extra  cost  in  the  long  run,  as 
they  are  much  more  durable  than  cast  iron  ones. 

The  "two-high"  mill  contains  two  rolls  carried  in 
"  housings  "  and  driven  in  opposite  directions  at  the  same 
rate.  A  single  roll,  as  it  is  cast  and  finished  ready  for 
insertion  in  the  housings,  consists  of  the  body  or  barrel, 
the  two  necks  or  journals  which  revolve  in  the  bearings, 
and  the  two  wobblers.  The  body  must  not  be  too  long 
compared  with  its  diameter,  as  it  would  bend  or  break 
under  the  heavy  stresses  put  upon  it.  The  usual  limits 
are  from  two  to  four  times  its  diameter.  The  two  rolls  are 


238  IEON  AND  STEEL. 

rarely  duplicates  except  for  square,  rectangular,  and  round 
sections.  They  are  cast,  and  then  turned  in  a  lathe  to  the 
necessary  shape. 

The  two  housings,  or  standards  in  which  the  rolls  work, 
and  by  which  they  are  kept  in  the  proper  relative  positions, 
are  massive  cast  iron  or  steel  frames  firmly  fixed  to  the 
bed  plate  by  means  of  pins  and  wedges,  and  further  held 
in  position  by  tie  rods  at  the  top  and  bottom.  The  bed 
itself  is  firmly  bolted  down  to  a  very  solid  foundation,  so  as 
to  be  practically  immovable.  The  masonry  of  the  founda- 
tion is  several  feet  thick,  and  the  bolts  or  pins  run  right 
through  it,  and  are  fastened  on  the  underside  by  plates  and 
nuts.  This  fixing  is  augmented  by  running  in  cement  all 
round  the  bed  plate.  The  chocks  which  carry  the  bearings 
are  fitted  loosely  into  the  housings  to  allow  for  expansion 
when  they  get  hot,  and  the  bearings  themselves  are  made 
of  gun  metal,  bronze,  or  white  metal.  The  space  in  the 
housings,  in  which  the  chocks  are  fitted,  should  be  large 
enough  to  allow  of  the  roll  being  drawn  through  endwise 
after  the  chocks  have  been  removed.  This  is  very  con- 
venient, and  saves  time  when  the  rolls  have  to  be  changed. 
The  bearing  far  the  bottom  roll  may  either  be  fitted  with 
a  chock  or  form  part  of  the  housing  itself,  but  the  bearing 
for  the  top  roll  must  be  arranged  so  that  it  can  be  moved 
up  and  down  during  working.  It  is  raised  or  lowered  with 
the  roll  by  the  movement  of  a  screw  passing  through  the 
top  of  the  housing.  To  do  this  the  chock  is  suspended  by 
rods  from  a  cross-piece  through  which  the  screw  passes. 
The  bottom  of  the  screw  is  expanded,  so  that  when  the 
screw  is  turned  upwards  the  projection  at  the  bottom 
catches  against  the  cross-piece  and  raises  it  together  with 
the  chock  and  roll.  But  when  the  screw  is  turned  down- 
wards it  passes  through  the  cross-piece,  and  coming  into 
contact  with  the  top  of  the  chock,  forces  it  down  and  the 
roll  with  it.  In  this  way  the  two  rolls  can  be  arranged  at  a 


MECHANICAL  TREATMENT   OF  IEON  AND   STEEL.     239 

given  distance  apart,  or  brought  into  contact  as  desired. 
The  bearing  in  the  chock  must  extend  round  the  neck  of 
the  roll  sufficiently  to  hold  the  roll  when  it  is  raised,  but  it 
is  seldom  that  the  bearing  extends  far  enough  round  in  one 
piece  to  grip  the  neck.  It  is  usually  in  three  pieces,  one 
at  the  top  and  one  on  each  side,  so  as  to  reduce  the  friction 
as  much  as  possible,  consistent  with  steady  working.  Very 
heavy  rolls  are  balanced  so  as  to  reduce  the  power  required 
to  raise  them,  and  also  the  shock  when  the  roll  drops  back 
after  a  pass. 

In  a  fully  equipped  mill  for  rolling  sections  there  are 
fittings  on  each  side  of  the  rolls  to  ensure  proper  working. 
When  the  bar  of  metal  is  presented  to  the  pass  between 
the  rolls  it  must  enter  properly,  or  it  will  probably  get 
between  the  collars  on  one  or  other  side  of  the  pass,  and 
damage  the  rolls.  To  prevent  this,  guides,  which  follow  the 
contour  of  the  rolls,  are  fixed  close  to  the  collars  of  each 
pass,  so  that  the  metal  is  forced  to  enter  the  pass  properly. 
There  is  also  a  fore  plate  parallel  with  the  rolls,  and  under 
the  guides,  over  which  the  metal  slides  on  entering  the  pass. 
There  is  always  a  tendency  for  the  hot  metal  to  stick  to 
one  or  other  of  the  rolls,  and  thus  to  wrap  round  it.  This 
must  not  happen,  so  the  top  roll  is  made  slightly  larger 
than  the  bottom,  one,  which  determines  that  the  metal  shall 
cling  to  the  lower  one  on  leaving  the  pass ;  it  is  then 
prevented  from  winding  round  the  roll  by  having  a  guard 
plate  sufficiently  close  to  and  following  the  contour  of  the 
bottom  roll.  This  directs  the  metal  outwards.  All  these 
fittings  are  not  necessary  for  every  rolling  operation. 

Driving  the  Rolls. — Since  the  top  roll  rises  and  falls 
when  at  work,  although  in  some  cases  this  motion  may  be 
small,  it  is  evident  that  the  connection  with  the  source  of 
power  cannot  be  perfectly  rigid.  Both  rolls  are  driven  in 
most  cases  to  ensure  uniform  working.  To  effect  this,  the 
wobblers  at  the  same  end  of  the  two  rolls  are  connected 


240  IRON  AND  STEEL. 

with  the  wobblers  of  a  pair  of  helical  pinions  by  short 
spindles  kept  in  position  by  two  coupling  boxes.  These 
boxes,  which  loosely  fit  the  spindle,  are  on  it  when  it  is 
brought  into  line  with  the  end  of  the  roll  and  the  end  of 
the  corresponding  pinion.  They  are  then  slipped  on  to  the 
wobblers,  and  are  prevented  from  moving  back  by  pieces  of 
wood  laid  along  the  exposed  part  of  the  spindle  and  bound 
to  it  by  iron  hoops.  A  sufficiently  loose  gearing  is  thus 
obtained  to  allow  of  easy  working.  As  both  rolls  are  fitted 
in  the  same  way,  and  the  two  pinions  are  geared  together, 
when  one  pinion  is  driven  both  rolls  revolve  and  in  opposite 
directions.  The  pinions,  which  are  in  effect  short  rolls, 
run  on  bearings  in  their  own  housings.  The  mill  is  usually 
driven  through  the  bottom  pinion  by  connecting  it  directly 
with  the  shaft  of  the  engine.  Coupling  boxes  and  a  spindle 
are  used  as  before.  The  helical  pinions  are  in  effect  open 
screws  with  their  axes  vertical,  so  that  the  teeth  come  into 
action  with  a  sliding  motion  that  produces  very  little  shock. 
Ordinary  cog-wheels  are  sometimes  used,  but  as  the  teeth 
must  be  strong  there  can  only  be  a  few  of  them,  and  the 
motion  produced  is  of  a  bumping  character. 

The  Pull-over  Mill. — The  original  method  of  working, 
and  one  that  is  still  largely  followed  for  light  work,  may 
be  described  as  follows :  one  end  of  the  hot  bar  to  be  rolled 
is  brought  on  to  the  fore  plate  by  the  workman,  called  the 
"roller,"  and  pushed  into  the  pass,  through  which  it  runs 
rapidly.  The  man  on  the  other  side,  the  "  catcher,"  then 
grips  it  with  a  pair  of  tongs  and  passes  it  back  over  the  top 
roll  to  the  roller,  who  pushes  the  end  into  the  next  pass. 
These  operations  are  repeated  until  the  rolling  is  finished. 
This  method  is  more  or  less  satisfactory  in  dealing  with 
light  sections,  for  the  workmen  are  very  expert  in  passing 
them  to  and  fro,  especially  when  they  are  on  "piece"  work; 
but  for  dealing  with  heavy  masses  of  hot  metal  lifting 
machinery  is  necessary,  and  time  is  wasted. 


MECHANICAL  TREATMENT   OF   IEON  AND   STEEL.     241 

The  Reversing  Mill. — One  way  of  saving  time  is  to  reverse 
the  rolls  at  each  pass  so  that  the  bar  may  be  passed  back- 
wards and  forwards  through  them  until  the  rolling  is 
finished.  In  rolling  heavy  ingots  the  bottom  roll  is  nearly 
level  with  the  floor,  and  a  number  of  auxiliary  rollers  are 
fitted  into  the  floor  in  front  of  the  roll  and  parallel  with  it. 
The  one  between  the  housings  is  driven  from  the  roll  itself 
and  takes  the  place  of  the  foreplate.  A  number  of  vertical 
bars  -are  arranged  between  the  rollers,  so  that  when  not  in 
use  their  upper  ends  are  below  the  general  level.  One  set 


PIG.  53.— A  Stand  of  Three-High  Eolls. 


A,  Housings. 

B,  Adjusting  screws. 
6',  Coupling  spindles. 


D,  Helical  gearing  rolls. 

E,  Driving  coupling  box. 


of  these  bars  can  be  forced  up  vertically  to  lift  an  ingot 
off  the  rollers  and  tilt  it  over.  These  are  the  "  tilters." 
Another  set  can  be  raised  and  then  moved  in  a  horizontal 
direction  between  the  rollers  so  as  to  push  the  ingot  side- 
ways. These  are  the  "  skids."  There  is  exactly  the  same 
arrangement  on  the  other  side  of  the  rolls.  Suppose  now 
that  a  red  hot  ingot  of  from  one  to  two  tons  is  dropped  on 
to  the  rollers,  it  is  first  tilted  and  skidded  into  the  proper 
position,  and  then  the  rollers  are  started  to  bring  it  to  the 
rolls,  through  which  it  passes.  The  rolls  are  then  reversed, 
and  it  is  passed  back  in  the  same  way.  This  is  repeated 
until  the  ingot  is  sufficiently  brought  down.  It  is  interesting 
i.s.  R 


242  IRON   AND   STEEL. 

to  see  the  rapidity  with  which  the  tilters  and  skids  deal 
with  large  masses  of  red  hot  metal. 

When  two  sets  of  rolls  are  used,  as  in  plate  rolling, 
travelling  tables,  fitted  with  live  rollers,  and  mounted  on 
wheels,  are  provided.  These  can  be  drawn  from  one  set  of 
rolls  to  the  next,  along  rails  laid  parallel  to  the  rolls.  The 
bar  to  be  rolled  into  a  plate  is  passed  backwards  and  for- 
wards through  the  one  set  of  rolls,  and  then  taken  to  the 
next  set  (usually  chilled  rolls)  to  be  finished.  This  is  easily 
effected  by  drawing  the  table  with  the  plate  on  it  in  front 
of  the  finishing  rolls. 

The  Three-High  Mill—Fig.  53.  In  a  mill  with  three 
rolls  the  return  pass  is  obtained  without  reversing,  which 
is  a  great  advantage  for  moderately  light  work.  The  three 
rolls  are  arranged  one  above  another  in  the  housings,  and 
are  geared  together  by  spindles  and  pinions  in  the  same 
manner  as  to  the  two-high  mill.  The  mill  is  driven  from 
the  middle  roll,  and  as  the  top  and  bottom  rolls  revolve  in 
opposite  directions  relatively  to  the  middle  one,  a  bar  may 
be  passed  between  the  bottom  and  the  middle  rolls  and 
back  again  between  the  middle  and  top  rolls.  The  bar  will, 
therefore,  only  have  to  be  raised  through  a  height  equal  to 
the  diameter  of  the  middle  roll  on  the  one  side,  and  lowered 
through  the  same  distance  on  the  other.  This  is  of  no 
importance  with  light  pieces,  but  with  heavy  ones  the 
necessary  lifting  apparatus  would  be  required.  This  form 
of  mill  was  first  used  in  America  in  1857,  and  has  been 
brought  to  great  perfection  there.  Some  of  the  largest 
American  mills  used  for  very  heavy  work  are  "three  high." 

Continuous  Mills  consist  of  a  number  of  two-high  mills 
arranged  in  tandem.  The  rolls  all  run  in  the  same  direc- 
tion, and  the  passes  between  them  gradually  decrease  in 
section  from  the  first,  where  the  metal  enters,  to  the  last, 
where  it  leaves  in  the  finished  state.  The  difficulty  with 
small  pieces  of  metal  is  to  keep  them  sufficiently  hot  for  the 


MECHANICAL   TREATMENT   OF   IRON   AND   STEEL.     243 

necessary  amount  of  work  to  be  put  into  them ;  and  it  is 
clear  that  the  more  rapidly  they  are  passed  through  the  pro- 
cess the  better.  In  the  continuous  process  different  parts  of 
the  bar  maybe  passing  through  several  mills  at  the  same  time. 
The  Looping  Mill  furnishes  a  good  example  of  rapid 
working.  It  consists  of  several  three-high  mills  arranged 
side  by  side  in  a  straight  line.  Suppose  that  telegraph 


FIG.  54. — Blooming  Shears. 

wire  is  being  rolled  in  this  mill.  The  bar  is  run  backwards 
and  forwards,  and  as  soon  as  it  can  be  bent  up  it  is  directed 
into  the  next  pass  above  before  it  is  through  the  last.  It  is 
then  pulled  down  into  the  next  pass  on  the  other  side,  and 
so  on.  The  bar  is  then  passing  through  the  rolls  in  a  series 
of  loops,  and  as  soon  as  the  end  is  through  the  last  pass  it 
is  carried  on  to  the  next  mill,  and  treated  as  before.  The 
operation  requires  expert  workmen,  but  it  takes  the  minimum 
time  for  completion. 

B  2 


244  IRON  AND   STEEL. 

In  a  complete  steel  mill  there  are  two  sets  of  operations. 
(1)  Cogging  or  blooming ;  (2)  Section  rolling.  At  one  time 
cogging  was  all  done  with  a  steam  hammer,  but  the  cogging 
rolls  have  now  largely  taken  its  place,  as  they  are  much 
more  economical  of  both  power  and  labour  per  ton  of  ingots 
treated.  Still,  first  cost  has  to  be  considered,  and  a  cogging 
mill  is  a  very  expensive  item ;  but  in  large  works,  where 
upwards  of  1,000  tons  of  ingots  are  put  through  per  week, 
there  is  no  doubt  as  to  its  success.  The  cogging  process  is 
used  for  ingots  varying  from  15  cwts.  to  4  tons.  They 
are  square  in  cross  section,  and  from  12  inches  to  22  inches 
on  the  side.  The  object  is  to  reduce  the  cross  section, 
increase  the  length,  and  improve  the  structure  by  putting 
work  into  the  metal.  The  cogging  rolls  vary  in  size  accor- 
ding to  the  general  run  of  ingots  to  be  passed  through  them. 
For  small  ingots  the  rolls  are  about  30  inches,  and  for  large 
ones  about  45  inches  in  diameter. 

The  ingot  is  brought  direct  from  the  soaking  pit  or  re- 
heating furnace,  and  passed  through  the  rolls  backwards 
and  forwards  until  it  is  reduced  to  the  required  section, 
which  may  be  either  square  or  rectangular.  When  the  bar 
is  square  and  6  inches  or  more  on  the  side,  it  is  called  a 
bloom ;  and  when  it  is  wider  than  it  is  thick  it  is  termed  a 
slab.  If,  however,  the  section  is  square  and  less  than 
6  inches  on  the  side,  the  bar  is  known  as  a  billet. 

Powerful  apparatus  for  shearing  blooms,  slabs,  and  billets 
is  required  for  economical  working.  When  an  ingot  has 
been  cogged  down  to  a  given  section,  its  weight  per  foot  of 
length  is  known,  and  if  it  is  then  taken  to  the  shears,  the 
imperfect  ends  can  be  chopped  off,  and  the  remainder  cut 
into  lengths  of  known  weight.  These  are  then  passed 
direct  to  the  ordinary  mill,  and  rolled  to  the  required  shape 
and  size  with  very  little  waste.  This  is  much  less  costly 
than  keeping  a  large  stock  of  moulds  of  different  sizes,  and 
attempting  to  cast  ingots  of  given  weights. 


MECHANICAL   TEEATMENT   OF   IRON  AND   STEEL.    245 


Fig.  54  represents  a  pair  of  powerful  blooming  shears 
with  live  rollers  for  carrying  the  blooms  forward.  The 
lengths  cut  off  are  regulated  by  the  use  of  stops  on  the 
further  side.  If  the  pieces  are  not  hot  enough  to  go  to  the 
finishing  rolls  they  are  reheated. 

The  number  of  shapes  into  which  steel  is  rolled  is  very 
large,  and  section  rolling  has  almost  developed  into  a  fine 
art.  Some  rolling  processes  are  very  ingenious,  and  are 
protected  by  patent  rights. 

Hail  llollincj. — The  making  of  a  railway  rail  is  a  good 
example  of  section  rolling,   and  will   serve    as    a  general 
illustration  of  the  process.     The  mill  used  in  this  country 
is  reversing,  and  the  reheated 
bloom   is  gradually  broken 
down  to  the  required  section. 
The  general  form  of  the  rolls 
is  shown  in  Fig.  52.     The 
numbers  represent  the  order 
in  which  the  passes  are  made. 
The  rail,  when  it  comes  from 
the   last    pass,    is    cut   into  FIG.  55. — Eail  Eolls. 

lengths  by  saws  while  still 

hot,  and  slowly  cooled.  It  is  then  pared  to  the  exact  length, 
straightened,  and  the  holes  for  the  fish  bolts  drilled  in  it 
simultaneously.  Each  rail  is,  therefore,  an  exact  duplicate 
of  its  fellows.  The  weight  of  the  rails  for  main  lines  is 
about  100  Ibs.  per  yard. 

Plate  and  Sheet  Rolling. — Slabs  are  used  for  conversion 
into  plates  and  sheets.  The  difference  between  the  two  is 
largely  a  matter  of  thickness,  for  plates  are  more,  and  sheets 
less,  than  J  inch  thick.  Plate  and  sheet  mills  are  furnished 
with  plain  rolls  and  accurate  adjusting  screws.  They 
require  considerable  experience  and  care  to  roll  to  exact 
size.  The  rolls  always  spring  a  little,  and  the  heavier  the 
pinch  put  upon  the  metal  between  them  the  more  they  give 


I 


2     I  3    4     5 


246  IKON  AND   STEEL. 

way.  This  causes  the  thickness  of  the  plate  to  vary  some- 
what in  parts.  Long  rolls  are  usually  turned  a  little  thinner 
in  the  middle,  and  all  rolls  used  for  this  kind  of  work 
require  frequent  redressing.  Armour,  ship,  and  boiler 
plates  are  largely  produced,  and  when  they  are  of  consider- 
able dimensions  require  heavy  auxiliary  apparatus  for 
handling,  straightening,  and  shearing  purposes.  Large 
plates  are  an  advantage  from  the  constructor's  point  of  view, 
but  there  are  limits  to  the  size,  such  as  the  weight  of  the 
ingot,  the  capacity  of  the  mill,  and  the  means  of  transport 
to  the  user.  Ship  plates  30  feet  long  and  4  feet  wide  are 
common,  and  boiler  plates  22  feet  long,  5  feet  wide,  and 
1J  inches  thick,  are  not  uncommon. 

Small  thin  sheets  are  still  largely  made  in  pull-over  mills. 
The  roller  and  his  underhand  keeps  the  sheets  going  through 
the  rolls  one  after  the  other.  The  roller  starts  the  first 
through  the  rolls,  and  follows  it  up  with  the  second.  By 
the  time  this  is  through  the  underhand  has  passed  the  first 
back  over  the  rolls,  and  this  goes  on  until  both  are  reduced 
to  the  required  thickness.  The  rolls  are  brought  nearer 
together  by  the  adjusting  screws  between  each  double  pass. 
When  thinner  sheets  than  can  be  rolled  singly  are  made, 
two  of  the  singles  are  placed  one  on  top  of  the  other  and 
rolled  together ;  while  for  still  thinner  sheets,  the  two  ends 
of  a  "  double  "  sheet  are  brought  together,  the  whole  pressed 
flat,  and  the  four  thicknesses  passed  through  the  rolls  after 
reheating,  if  necessary.  The  single  sheets  in  the  pack 
usually  stick  together,  and  are  then  separated  by  passing 
through  a  machine  which  breaks  up  the  film  of  oxide 
between  them.  Sheets  that  are  to  have  a  clean  bright 
surface  are  pickled  in  dilute  sulphuric  acid,  dried,  and 
passed  through  smooth  chilled  rolls,  by  which  the  surface  is 
brought  up.  Cold  rolling  is  not  much  resorted  to  except 
when  a  bright  finish  is  desired,  or  when  the  dimensions  of 
the  section  must  be  accurate,  as  in  the  case  of  shafting.  In 


MECHANICAL   TEEATMENT   OF   IRON  AND   STEEL.     247 

rolling  to  size,  it  is  to  be  remembered  that  the  exact  dimen- 
sions of  the  finishing  pass  depend  on  the  temperature  of  the 
rolls,  and  those  of  the  finished  section,  on  the  temperature 
from  which  it  cools.  The  higher  this  temperature  the 
smaller  will  the  section  be  when  cold.  Therefore,  for 
exact  work,  the  piece  must  be  brought  down  to  the 
approximate  section  while  hot,  and  finished  in  chilled  rolls 
when  cold. 

Rod  Rolling. — No  operation  in  the  mechanical  treatment 
of  iron  and  steel  has  undergone  so  much  development  as 
that  of  rod  rolling.  It  will  be  readily  understood  that  much 
breaking  down  is  required  in  converting  a  short  thick  billet 
into  a  very  long  thin  rod.  Also,  that  the  thinner  the  rod 
becomes  the  more  rapidly  will  its  parts  cool,  and,  therefore, 
the  faster  must  the  operation  be  carried  on.  A  square  billet 
cannot  be  broken  down  at  once  into  a  round  rod,  but  must 
be  gradually  made  to  take  the  final  shape  as  it  increases  in 
length.  In  the  case  of  rounds,  the  spring  of  the  rolls  causes 
the  section  not  to  be  truly  circular,  but  this  defect  diminishes 
as  the  rod  thins  down.  A  very  long  thin  rod  approximates 
to  a  wire  in  character,  but  it  is  not  strictly  so,  although  it 
is  sometimes  called  wire  when  used  for  rough  purposes,  such 
as  fencing.  But  iron  or  steel  wire  is  first  rolled  hot,  and 
then  cold  drawn  through  a  plate  to  the  required  gauge. 
The  looping,  or  Belgian  mill,  has  already  been  mentioned, 
and  is  largely  used  for  rolling  long  rods.  A  three-high 
mill  or  its  equivalent  must  be  used,  as  the  loops  form  on 
both  sides.  As  the  section  decreases  the  rod  runs  through 
faster,  and  the  loops  become  longer,  so  that  they  have  to  be 
run  out,  and  this  requires  extra  labour,  with  more  floor 
space.  The  free  end,  when  it  leaves  the  last  pass,  is  attached 
to  a  reel,  and  the  rod  wound  on  as  fast  as  it  comes  through. 
Thus  the  rod  is  in  a  coil  when  finished.  The  free  end  of  the 
rod,  as  it  issues  from  a  pass,  is  caught  and  twisted  before  it 
is  presented  to  the  next.  In  this  way  the  sides  are  brought 


248  IEON  AND   STEEL. 

to  the  top  and  bottom  of  the  next  pass,  and  a  more  uniform 
section  is  obtained. 

Bedson,  of  Birmingham,  adapted  the  continuous  mill 
very  successfully  to  rod  rolling,  and  it  is  now  used  in  a 
more  or  less  modified  form  both  in  this  country  and 
in  America.  Now  it  is  evident  that  the  smaller  the  section 
of  the  part  of  the  rod  running  through  a  given  pair  of  rolls, 
the  faster  must  they  run  in  order  to  take  in  the  increasing 
length  of  rod  coming  through  the  pair  behind  them.  To 
meet  this  difficulty  the  rolls  are  geared  to  the  main  driving 
shaft  in  such  a  way  that  succeeding  pairs  run  faster  in  the 
same  proportion  as  the  rod  lengthens.  Also,  alternate  pairs 
are  run  vertically,  so  that  the  rod  is  presented  at  right 
angles  to  each  succeeding  pass.  Difficulties  were  met  with 
in  working  the  original  mill  that  have  been  overcome  in  the 
modified  forms ;  while  the  winding  on  the  reel  at  the  end 
has  been  made  automatic.  The  billets  are  brought  straight 
from  the  reheating  furnace  to  the  first  pass,  and  the  rod  is 
rolled  through  to  the  last.  The  energy  of  the  rolls  appears 
largely  as  heat  in  the  rod,  and  the  operation  is  carried  on  so 
rapidly,  that  when  it  leaves  the  mill  the  rod  is  nearly  as 
hot  as  the  original  billet  was  on  entering,  and  this  in  spite 
of  the  fact  that  the  rolls  are  cooled  with  water.  During  the 
cooling  of  the  coil  on  the  reel  the  surface  is  oxidised  and 
scale  formed  ;  to  prevent  this  the  rod  is  sometimes  passed 
through  water  before  it  reaches  the  reel.  In  the  case  of 
medium  carbon  steel  rod  the  cooling  is  regulated  so  as  not 
to  harden  the  metal  sufficiently  to  necessitate  its  being 
annealed  before  being  drawn  into  wire. 

The  length  of  rod  in  one  coil  varies  considerably,  and 
may  be  as  much  as  600  yards.  It  is  often  rolled  down 
to  J  inch  in  diameter  when  it  is  to  be  used  for  wire 
drawing. 

Wire  Drawing  is  a  very  ancient  process,  and  consists  in 
drawing  the  piece  of  metal  through  a  series  of  holes  of 


MECHANICAL   TEEATMENT   OF   IRON  AND   STEEL.    249 


250  IRON  AND   STEEL. 

gradually  decreasing  size  in  a  draw  plate,  until  it  is  reduced 
to  the  required  diameter.  If  the  thickness  to  be  reduced  is 
considerable,  the  wire  will  require  annealing  one  or  more 
times  during  the  process,  as  it  is  hardened  and  rendered 
brittle  by  the  work  put  upon  it.  But  this  may  not  be  neces- 
sary with  iron  or  steel  wire,  if  it  is  first  reduced  by  hot  rolling. 
In  a  continuous  wire  drawing  machine,  which  is  the  latest 
development  in  this  direction,  a  series  of  vertical  dies  and 
horizontal  drums  are  arranged  in  line,  and  the  coil  of  rod  is 
placed  on  a  loose  reel  at  one  end.  The  rod  is  started 
through  the  first  die  and  wrapped  round  the  first  drum 
several  times ;  it  is  then  passed  through  the  second  die  to 
the  second  drum,  and  so  on  through  the  series.  The  free 
end  is  then  connected  with  the  winding  reel,  which  is 
revolved  with  sufficient  force  to  draw  the  wire  through  the 
last  die.  The  different  drums  are  revolved  at  varying  speeds 
to  compensate  for  the  increasing  length  of  the  wire,  and 
each  drum  draws  the  wire  through  the  preceding  die.  In 
this  way  the  pull  is  distributed  and  no  part  of  the  wire  is 
unduly  strained.  The  rod  must  be  carefully  pickled  in 
dilute  sulphuric  acid  to  remove  the  scale,  passed  through 
lime  water  to  remove  excess  of  acid,  swilled,  and  dried. 
Unless  this  is  done  the  hard  scale  will  injure  the  dies,  and 
the  wire  will  be  defective.  The  number  of  dies  is  regulated 
by  the  thickness  of  the  wire,  and  how  much  it  can  be 
reduced  without  annealing.  The  wire  as  it  comes  from  the 
machine  is  hard,  and  if  wanted  soft  has  to  be  annealed. 
Common  wire  is  often  annealed  in  the  ordinary  furnace,  and 
a  scale  is  formed  on  its  own  face.  This  can  be  avoided 
by  close  annealing  in  an  iron  pot.  Both  hard  and  soft  wire 
are  put  on  the  market. 

Steel  Forging. — The  tilting  of  tool  steel  has  long  been 
practised,  and  for  some  purposes  gives  better  results  than 
rolling.  It  is  now  carried  out  with  small  steam  hammers 
in  a  very  effective  manner.  For  large  forgings,  hammers  of 


MECHANICAL   TREATMENT   OF   IRON  AND   STEEL.    251 

corresponding  size  have  to  be  used ;  but  with  a  considerable 
thickness  of  metal  the  blow  is  not  sufficiently  penetrating, 
and  the  centre  has  little  or  no  work  put  into  it.  Still,  many 
large  pieces  are  forged  into  shape  under  the  hammer  for 
engineering  purposes.  But  much  more  effective  work  is 
done  by  the  forging  press,  especially  with  large  masses  of 
metal.  The  pressure  lasts  long  enough  for  its  effect  to 
extend  to  the  centre  of  the  mass.  These  presses  are  now 
used  in  all  the  large  steel  works.  One  in  regular  work  at 
Messrs.  Firth's,  Sheffield,  exerts  a  pressure  equal  to  3,000 
tons,  and  is  worked  by  engines  of  1,200  h.-p.  The  writer 
had  the  pleasure  of  seeing  this  powerful  tool  at  work  on  a 
20- ton  ingot  that  was  being  drawn  out  under  it. 

There  are  a  number  of  hydraulic  presses  in  use,  which  vary 
in  construction  and  detail  of  working,  but  in  all  of  them  the 
pressure  put  on  the  work  is  exerted  by  water  in  a  hydraulic 
cylinder,  the  ram  of  which  moves  downwards.  The  head  of 
the  ram  carries  the  pallet  which  comes  into  contact  with 
the  forging.  Auxiliary  cylinders  are  required  for  raising 
the  ram  after  it  has  worked  through  its  stroke.  In  some 
forms  accumulators  are  used,  into  which  water  is  forced 
under  a  dead  weight ;  in  others,  direct  acting  pumps  supply 
the  pressure  ;  and  in  others  a  long  piston  of  small  section  is 
forced  from  a  steam  cylinder  into  the  pressing  cylinder  to 
drive  the  ram  to  its  work.  Very  strong  cylinders  of  cast  or 
forged  steel  are  necessary  to  withstand  the  enormous  pres- 
sure of  four  tons  per  square  inch  used  in  some  of  these  presses, 
and  the  valves  and  collars  must  be  as  perfect  as  possible. 
The  best  forms  of  the  press  are  under  perfect  control. 

Large  ingots  are  not  usually  cast  square  in  section, 
but  in  the  form  of  a  hexagon  with  slightly  fluted  sides,  as 
they  then  take  the  forging  better.  On  account  of  the  slow 
rate  of  cooling  of  such  large  masses,  segregation  of  phos- 
phides and  sulphides  may  take  place  to  a  hurtful  extent. 
Also,  there  is  more  liability  to  unequal  distribution  of 


252 


IRON  AND  STEEL. 


MECHANICAL  TREATMENT  OF  IRON  AND  STEEL.     253 

strains  in  the  solidifying  mass,  and  to  the  formation  of 
dangerous  flaws.  Eeheating  has  to  be  carried  out  most 
carefully,  especially  with  the  higher  carbon  steels.  Thus  a 
50-ton  ingot  will  require  to  be  soaked  for  two  or  three  days 
before  removal  to  the  press.  The  porter  bar,  which  holds 
the  ingot  while  it  is  in  the  press,  is  a  heavy  bar  with  a 
collar  that  is  fastened  to  one  end  of  the  ingot  before  it  is 
put  into  the  reheating  furnace.  The  collar  is  outside  the 
furnace,  and  the  space  round  the  ingot  is  filled  in  to  pre- 
vent the  admission  of  air.  Siemens  reversing  gas  furnaces 
are  used  for  reheating  large  ingots.  At  the  back  of  the 
collar  is  a  wheel  round  which  an  endless  chain  passes  to  a 
pulley  above,  which  is  suspended  from  a  travelling  crane. 
The  pulley  is  arranged  so  that  it  can  be  rotated,  together 
with  the  porter  bar  and  the  ingot.  This  is  used  to  move 
the  ingot  round  when  it  is  in  the  press.  Both  solid  and 
hollow  forgings  are  made  in  these  presses.  The  general 
details  of  the  plant  are  well  brought  out  by  the  photograph 
of  a  3,000-ton  press  shown  in  Fig.  56,  which  has  been  kindly 
supplied  by  Messrs.  Firth. 

The  general  arrangement  of  a  rolling  mill  is  shown  in 
Fig.  57. 

When  two  pieces  of  iron  or  steel  are  welded  together  the 
success  of  the  operation  depends  upon  the  plasticity  of  the 
metal  at  a  welding  heat.  In  this  condition  pressure  exerted 
either  by  hammering  or  squeezing  causes  the  particles  on 
the  surfaces  in  contact  to  interpenetrate,  and  a  sound  joint 
is  the  result.  The  surfaces  must  be  clean,  and  to  ensure 
this  silica  sand  is  sprinkled  on  the  hot  iron,  while  borax  is 
used  for  steel.  In  this  way  the  oxide  formed  during  the 
heating  is  converted  into  a  fluid  slag  which  is  squeezed 
from  between  the  surfaces  and  a  clean  contact  obtained. 
It  is  a  fact  difficult  to  explain  that  ingot  metal  will  not  weld 
properly,  and  so  is  rarely  welded. 


CHAPTEE  X. 

PHYSICAL    AND    MECHANICAL     PROPERTIES    OF     IRON    AND    STEEL. 

IRON  in  its  various  forms  is  used  for  so  many  and  such 
diverse  purposes,  that  careful  testing  by  various  methods 
is  necessary  to  determine  the  suitability  or  otherwise  of  a 
particular  variety  of  the  metal  for  a  given  purpose,  and  in 
constructive  work  particularly  to  determine  the  limit  of  safety. 
Iron,  in  common  with  other  metals,  possesses  a  number  of 
physical  and  mechanical  properties,  some  of  which  are 
peculiar  to  metallic  bodies,  and  its  usefulness  for  a  given 
purpose  is  often  determined  by  the  possession  of  one  or 
more  of  the  properties  in  a  high  degree.  The  most  impor- 
tant of  these  properties  are  tenacity,  elasticity,  ductility, 
malleability,  toughness  and  hardness. 

Tenacity  is  the  property  by  which  the  particles  of  the 
metal  cling  together  so  as  to  resist  separation  by  forces 
acting  in  opposite  directions  along  their  common  axes. 
This  tenacity,  tensile  strength,  or  ultimate  strength  is 
measured  by  the  magnitude  of  the  forces  acting  through  a 
cross  section  of  unit  area.  The  sum  of  these  forces  makes 
up  the  breaking  stress,  which  is  expressed  in  this  country  in 
either  tons  or  pounds  to  the  square  inch  of  cross  section, 
and  on  the  continent  in  kilograms  per  square  centimetre. 
The  forces  making  up  this  breaking  stress  are  represented 
by  a  dead  weight,  and  are,  therefore,  static  in  character. 
They  are  uniformly  distributed  over  the  cross  section,  and 
act  at  right  angles  to  it,  so  that  whatever  may  be  the  area 
of  the  cross  section  the  magnitude  of  the  forces  will  be 
proportional  to  it.  The  method  of  testing  is  to  strain  a  bar 


MECHANICAL  PROPEETIES   OP  IRON  AND   STEEL.     255 

or  wire  of  known  length  and  cross  section,  by  gradually 
increasing  stresses  in  the  direction  of  its  length  until  it 
breaks.  Thus  the  magnitude  of  the  forces  distributed  over 
J square  inch  would  be  one  quarter  of  that  for  1  square  inch,  or 
one  quarter  the  stress  would  be  required  to  break  the  J  inch 
section  as  would  be  required  for  the  1  inch  section.  That 
is,  whatever  may  be  the  cross  section  of  the  test  bar  if  the 
breaking  stress  is  known,  it  can  be  calculated  to  that 
required  for  a  bar  of  unit  cross  section.  The  bars  may  be 
of  any  shape  as  long  as  the  section  is  uniform,  but  round, 
square,  and  rectangular  bars  are  commonly  used,  as  it  is 
easy  to  compute  their  cross  section. 

The  simple  rules  for  determining  cross  section  of  bars 
may  be  stated  as  follows  :— 

For  a  square  bar  of  side  "  a  "  the  cross  section  =  a  X  a 
For  a  rectangular  bar  of  sides  "a"  and  "b" 

the  cross  section  =  a  X  b 

For  a  circular  bar  of  diameter  "  d  "  the  cross 

section  =  d  X  d  X  ()'7S54. 

Elasticity. — This  important  property  governs  the  recovery 
of  form  after  the  removal  of  a  stress  insufficient  to  produce 
rupture.  All  bodies  are  more  or  less  distorted  when  a 
stress  is  applied  to  them,  and  the  greater  the  stress  the 
greater  the  distortion.  Also,  all  bodies  recover  their  form 
more  or  less  after  the  stress  is  removed.  A  perfectly 
elastic  body  would  recover  itself  immediately  and  com- 
pletely ;  but  solid  bodies  are  not  by  any  means  perfect  in 
this  respect,  and  the  stress  causes  a  kind  of  fatigue  in  that 
the  last  portions  of  the  strain  die  out  slowly,  and  the  body 
only  recovers  itself  completely  after  some  time.  If,  how- 
ever, the  stress  exceeds  a  certain  limit  for  a  given  body  the 
body  is  unable  to  recover  itself  even  in  time,  and  is 
permanently  deformed.  This  gives  rise  to  the  terms 
elastic  limit  and  permanent  set.  The  determination  of  the 
elastic  limit  is  most  important,  as  the  limit  of  safety  lies 


256  IKON  AND   STEEL. 

well  within  it.  In  practice  the  elastic  limit  never  falls 
below  50  per  cent,  of  the  tensile  strength,  and  as  it  is 
difficult  to  determine  the  former  during  rapid  commercial 
testing,  the  tensile  strength  is  relied  upon  to  furnish 
sufficient  information  for  the  purpose.  But  the  yield  point, 
which  is  in  the  neighbourhood  of  the  elastic  limit,  can  be 
determined  on  commercial  machines,  and  furnishes  a  very 
desirable  check. 

Within  the  limit  of  elasticity  the  increase  or  decrease  in 
the  length  of  a  uniform  bar  is  proportional  to  the  applied 
stress,  and  it  is  easy  to  imagine  the  bar  increased  to  twice 
its  length  or  decreased  to  zero  without  the  limit  being 
passed.  The  calculated  stress  that  would  be  required  to 
effect  this  lengthening  or  shortening  is  called  the  modulus 
of  elasticity  or  Young's  Modulus.  If  E  denote  the  modulus, 
S  the  stress  on  unit  area,  and  E  the  extension  or 
compression, 

S 
Then  E  =  ^5  =  modulus  of  elasticity. 

In  the  case  of  hardened  steel  the  extension  to  the  limit 
is  small  and  the  load  great.  Thus  the  load  on  a  bar  of 
1  inch  cross  section  is  62  tons,  and  the  extension  per  linear 
inch  is  0'00418  inch. 

=  14>882 


The  idea  is  practically  impossible,  but  it  is  sometimes 
very  useful  from  a  theoretical  point  of  view. 

Ductility  is  the  property  of  the  metal  that  allows  its 
particles  to  flow  under  lateral  pressure.  In  wire  drawing 
this  pressure  is  exerted  by  the  sides  of  the  hole  in  the  die 
through  which  the  metal  is  drawn  by  a  tensile  stress 
applied  at  one  end.  Now,  when  the  stress  is  applied  at 
both  ends,  and  there  is  no  lateral  pressure,  the  bar  thins 
down  in  the  middle  and  towards  the  two  ends.  This  causes 


MECHANICAL  PEOPEETIES  OP  IRON  AND  STEEL.     257 

it  to  increase  in  length  and  decrease  in  cross  section.  An 
actual,  though  small  lengthening  takes  place  within  the 
elastic  limit,  and  constitutes  the  temporary  deformation 
from  which  the  bar  recovers  on  removal  of  the  stress.  But 
when  the  limit  is  passed  the  elongation  is  permanent  and 
goes  on  increasing  until  the  bar  breaks.  Thus,  if  the 
length  of  the  bar  being  tested  is  measured  before  and  after 
rupture,  the  amount  of  elongation  is  known  and  can  be 
calculated  as  a  percentage  of  the  length  under  stress.  This 


FIG.  58. — Diagram,  of  Tensile  Testing  Machine. 

gives  the  elongation  per  cent.  Similarly  the  area  of  the 
fractured  surface  can  be  measured  and  the  reduction  of  area 
per  cent,  obtained.  Some  authorities  consider  the  elonga- 
tion the  more  important,  but  the  reduction  of  area  is  a  good 
measure  of  tensile  ductility  or  toughness.  After  the  elastic 
limit  is  passed  the  bar  elongates  appreciably  without 
further  increase  in  the  stress.  This  is  known  as  the  yield 
point.  After  this  is  passed  if  the  stress  is  increased  slightly 
the  bar  thins  down  and  breaks.  The  actual  breaking  stress 
is  less  than  the  ultimate  strength  of  the  bar  because  it 


i.s, 


258 


IEON  AND   STEEL. 


has  thinned   down,  and  fractures  across  a  smaller  cross- 
section. 

The  Tensile  Testing  Machine. — The  various  measurements 
mentioned  above  are  made  during  a  single  test  with  a 
properly  equipped  machine.  There  are  various  machines 
in  practical  use,  and  in  the  larger  ones  the  stress  is  applied 
at  one  end  of  the  bar  by  a  hydraulic  ram,  and  balanced  at 


FIG.  59.-  Tensile  Testing  Machine  in  Position. 

the  other  by  a  weighted  lever  which,  acting  like  a   scale 
beam,  measures  the  stress  in  dead  weight. 

The  general  principles  of  Wicksteed's  machine,  which  is 
largely  used  in  this  country,  are  shown  in  Fig.  58.  A  long 
lever  bar,  AB,  is  supported  on  a  fulcrum  at  F,  on  which 
it  can  move  freely.  The  ratio  of  the  two  arms  A  F,  B  F  is 
1  to  50,  so  that  a  dead  weight  of  1  ton  at  B  would  balance  a 
stress  of  50  tons  at  A.  Directly  under  A  is  a  hydraulic 


MECHANICAL   PROPERTIES   OF   IRON  AND  STEEL.     259 

cylinder,  to  the  ram  of  which  a  grip  is  attached.     A  second 
grip  is  suspended  from  A,  and  a  bar  placed  in  them  and 
pulled  tight  is  in  a  vertical  position.     Fastened  on  to  the 
bar  near  the  grips  are  two  clips,  the  upper  one  of  which 
carries  a  small  pulley.     An  inextensible  thread  passes  from 
the  bottom  clip  over  the  pulley  to  a  second  pulley,  and  then 
down  to  and  several  times  round  a  pulley  attached  to  the 
drum.      The    free    end    is    attached  to   a  weight   which, 
hanging  down,  keeps  the  whole  of   the  thread   tight.     A 
small  hydraulic  cylinder  directly  connected  with  the  main 
cylinder,  and  therefore  sharing  its  pressure,  is  arranged  so 
that  its  ram  moves  out  in  a  horizontal  direction  carrying 
with  it  a  pointer  that  presses  lightly  against  the  surface  of 
the  drum.     The  pointer  is  kept  in  position  by  a  spring,  and 
can  only  move  in  a  horizontal  direction.    The  surface  of  the 
drum  is  covered  by  a  sheet  of  squared  paper.     The  bar  to 
be  tested  is  measured  and  fixed  on  the  grips  of  the  machine 
so  that  the  parallel  marks  on  the  ends  of  the  bar,  between 
which  the  length  to  be  stressed  is  measured,   just  show 
outside  the  faces  of  the  grips.     The  clips  and  thread  are 
then  arranged,  and  the  pressure  applied  by  forcing  water 
into  the  cylinder,  either  by  a  pump  or  an  accumulator.     As 
the  bar  stretches  the  thread  moves  over  the  pulley  and 
causes  the  drum  to  rotate,  while  the  increased  pressure  in 
the  small  cylinder  drives  the  pointer  over  the  surface  in  a 
horizontal  direction.      These  two  motions  are  combined, 
and  the  pointer  traces  a  curve  on  the  squared  paper.     Thus 
the  exact  nature  of  the  elongation  is  known.     As  long  as 
the  strain  is  within  the    elastic   limit  the  stress   is    pro- 
portional  to   it.      After   the    limit   is   passed   the    strain, 
elongation  increases  more  rapidly,  and  this  goes  on  until 
the    bar   breaks.     While    the    stress    and    strain   are    pro- 
portional the  pointer  traces  a  straight  line,  but  when  the 
proportionality  ceases  the  straight  line   becomes  a  curve, 
and  it  is  evident  that  the  stress  at  this  point  is  the  measure 

s  2 


260 


IKON  AND   STEEL. 


of  the  elastic  limit,  but  it  is  difficult  to  tell  exactly  where 
the  straight  line  passes  into  the  curve.  The  yield  point, 
however,  is  clearly  shown.  After  the  bar  is  broken  the 
increase  in  length  and  the  reduction  in  area  are  measured. 
It  is  thus  possible  to  obtain  the  four  quantities,  tensile 
strength,  elastic  limit,  elongation,  and  reduction  of  area ; 
and  these  are  usually  determined.  A  rough  indication  of 


FIG.  60. 

the  nature  of  a  stress-strain  diagram  is  shown  above  the 
drum  in  Fig.  58.  Fig.  59  is  an  illustration  of  a  modern 
tensile  testing  machine.  Its  capacity  is  from  50  to  100  tons. 
The  sliding  weight  is  propelled  along  the  beam  by  means 
of  a  screw  worked  by  power,  and  for  the  fine  adjustment  by 
a  hand  wheel  fixed  to  the  column.  The  graduated  scale 
on  the  beam  is  fitted  with  a  vernier  by  which  sub-divisions 
of  1- 100th  of  a  ton  can  be  read.  The  hydraulic  cylinder 
by  which  the  stress  is  applied  is  seen  on  the  right  of  the 


MECHANICAL   PROPERTIES   OF   IEON  AND   STEEL.     261 


Ai 


column.  There  is  a  300-ton  Wicksteed  machine  at  the 
National  Testing  Laboratory,  Paris.  A  similar  machine  is 
also  in  course  of  construction  by  Messrs.  Avery  for  the 
Birmingham  University.  These  powerful  machines  can  be 
used  for  a  variety  of  tensile,  transverse,  bending  and 
torsional  tests  of  constructive  iron  and  steel. 

Fig.  60  is  a  photograph  of  a  number  of  test  pieces  that 
have  been  broken  in  a  tensile  machine.  The  bottom  pair  were 
exact  duplicates  before  the  upper  one  was 
tested.     They  show  clearly  the  effects  of 
the  stress  on  the  length  and  cross-section 
of  the  piece. 

Resistance  to  Torsion  is  an  important 
property,  and  is  readily  determined.  One 
end  of  the  test  bar  is  rigidly  fixed  in  the 
machine,  and  the  other  end  is  made  fast 
to  the  centre  of  a  wheel,  with  its  axis  at 
rig! it  angles  to  the  plane  of  the  wheel. 
When  the  wheel  is  turned  the  bar  is 
twisted,  and  the  resistance  to  this  twist  is 
proportional  to  the  force  required  to  pro- 
duce it.  The  test  is  not  usually  carried 
beyond  the  limit  of  elasticity,  and  readily 
indicates  any  lamination  which  may  exist 
in  the  material  being  tested. 

Resistance  to  Crushing.  —  A  crushing 
force  acts  in  just  the  opposite  direction  to  a  tensile  force, 
and  the  test  is  usually  made  upon  the  metal  used  for 
columns  which  have  to  carry  a  dead  weight  on  their  upper 
ends.  Both  cast  iron  and  structural  steel  are  tested  in  this 
way.  The  test  is  carried  out  with  a  tensile  testing  machine, 
but  the  test  piece,  C,  a  short  cylinder,  is  put  between  the 
moving  parts,  Ab  A2,  of  a  pair  of  shackles,  which  are  so 
arranged  in  the  grips  of  the  machine  that  when  the  pressure 
is  put  on  the  moving  pieces  are  drawn  closer  together,  and 


FIG.  61.— 
Shackles. 


262 


IEON  AND   STEEL. 


crush  the  test  piece  between  the  hard  steel  blocks,  BI,  B2. 
The  test  cylinders  are  usually  small,  about  J  inch  in 
diameter,  and  the  length  is  from  one  to  three  times  the 
diameter.  Steel  test  pieces  usually  bulge,  and  the  resistance 
to  crushing  is  judged  by  the  deformation  ;  but  cast  iron 
usually  fractures,  and  the  mode  of  fracture  is  generally 
a  shear  at  an  angle  of  56°  with  the  vertical  axis  of  the 
cylinder.  The  form  of  the  shackles  is  shown  in  Fig.  61. 
Transverse  Strength. — Tests  for  determining  the  resistance 
to  transverse  stress  are  commonly  used  for  cast  iron,  and 
are  carried  out  with  a  transverse  testing  machine.  The  test 

bar  is  held  by  two 
dogs  or  eye-pieces 
so  fitted  to  the 
base  of  the  ma- 
chine that  they  can 
be  adjusted  one  on 
each  side  of  the 
centre  pillar,  and 
at  a  regulated  dis- 
tance apart.  A 
screw  passing 
through  the  top  of 

the  pillar  can  be  forced  downwards  by  a  hand  wheel  con- 
nected directly  with  the  top  of  the  screw.  This  presses  a 
steel  knife  edge  on  the  short  arm  of  a  lever  bar,  the  fulcrum 
of  which  is  inside  the  pillar.  The  pressure  is  balanced  by  a 
sliding  weight  on  the  long  arm  of  the  lever.  As  the  screw 
is  revolved  it  raises  a  connecting  rod,  to  the  end  of  which 
a  stirrup  is  suspended  through  which  the  test  bar  passes. 
The  dogs  are  fixed  at  a  regulated  distance  apart,  and  the 
stirrup  is  exactly  midway  between  them,  so  that  as  the  con- 
necting rod  moves  upwards  the  test  bar  is  pulled  up  against 
the  dogs,  and  a  steady  upward  pressure  is  exerted  upon  it 
at  its  centre.  This  pressure  is  balanced  and  measured  by 


FIG.    62. — Diagram   of    Transverse    Testing 
Machine. 


MECHANICAL  PROPERTIES  OF  IRON  AND  STEEL.     263 

the  sliding  weight,  and  when  it  just  exceeds  the  transverse 
strength  of  the  test  bar,  the  bar  breaks.  The  exact  dead 
weight  stress  is  measured  by  the  position  of  the  sliding 
weight  on  the  lever  arm.  The  ordinary  test  bars  are  3  feet 
6  inches  long,  2  inches  wide,  and  1  inch  thick.  They  are 
placed  in  the  machine  with  the  supports  3  feet  apart  and 


FIG.  63. — Transverse  Testing  Machine. 

with  their  broad  sides  vertical.  The  transverse  strength  of 
cast  iron  bars  of  this  section  varies  from  25  to  40  cwts. 
according  to  the  quality  of  the  metal.  But  test  bars  of 
various  dimensions  are  used  according  to  the  power  of  the 
machine.  The  pressure  is  always  applied  by  the  hand  wheel. 
Fig.  62  shows  the  general  principle  of  the  machine,  and 
Fig.  63  is  an  illustration  of  Avery's  combined  tensile  and 
transverse  testing  machine,  which  has  been  found  very  useful 


264 


IKON  AND   STEEL. 


for  foundry  purposes.  It  will  exert  a  transverse  stress  up 
to  36  cwts.,  and  a  tensile  stress  of  fourteen  tons  per  square 
inch  on  a  round  bar  J  inch  in  diameter,  and  of  fifty  tons 
per  square  inch  on  a  bar  J  inch  in  diameter. 

Dynamic    Testing. — Much  useful  information  about  the 


FIG.  64. — Pendulum.  Drop  Test  Machine. 

strength  of  materials  is  obtained  by  the  static  tests  described 
above ;  but  it  is  also  necessary  that  dynamic  tests  should 
be  applied  in  cases  where  the  material  is  to  be  used  for  the 
construction  of  moving  parts  continually  exposed  to  dynamic 
stresses,  or  for  fixed  parts  exposed  to  a  series  of  shocks.  A 
railway  axle  and  rail  are  typical  examples. 


MECHANICAL   PROPERTIES   OF   IRON  AND   STEEL.     265 

The  Drop  Test. — This  well-known  test  is  used  for  axles, 
rails,  and  tyres.  The  machine  for  carrying  it  out  consists 
of  two  standards  between  which  a  heavy  mass  of  iron,  the 
tup,  or  monkey,  usually  weighing  one  ton,  can  be  raised  to 
a  given  height,  and  then  allowed  to  fall  on  to  the  test  piece 
below.  The  rail  or  axle  is  placed  on  supports  fixed  at  a 
regulated  distance  apart,  and  the  tup  raised  to  the  proper 
position,  where  it  is  secured  by  a  catch.  On  being  released, 
it  falls  and  delivers  a  blow  to  the  test  piece,  the  magnitude 
of  which  depends  upon  the  height  from  which  it  falls. 
This  is  repeated  several  times  according  to  the  nature  of 
the  test.  The  bar  is  turned  up  after  each  blow,  so  that 
alternate  blows  are  delivered  on  opposite  sides  of  it.  In  a 
good  test  the  rail  or  axle  is  bent  by  the  first  blow, 
straightened  by  the  second,  and  so  on ;  it  should  show  no 
signs  of  fracture  at  the  end  of  the  operation.  Thus  an  axle 
4f  inches  in  diameter  should  not  fail  under  five  blows  from 
a  tup  weighing  one  ton,  and  falling  through  a  distance  of 
20  feet.  With  bars  of  smaller  diameter  the  height  of  the 
drop  is  decreased.  Now  one  ton,  in  falling  through  a  height 
of  20  feet,  would  develop  during  its  fall  2,240  X  20  =  44,800 
foot  pounds  of  energy,  which  is  the  measure  of  the  blow 
delivered  to  the  test  bar. 

For  tyre  testing  the  tyre  is  placed  in  the  running  position 
under  the  weight,  and  distorted  by  repeated  blows.  Some- 
times this  test  is  made  in  a  hydraulic  press.  For  the  above 
tests  it  is  usual  to  select  the  test  pieces  haphazard  from  a 
number  of  the  rails,  axles,  or  tyres  made  from  the  same 
material.  They  are  not  put  to  work  after  the  test. 

Modifications  of  the  drop  test  have  also  been  described. 
In  one  of  these  used  by  Messrs.  Seaton  and  Jude  the  test 
piece  is  a  small  notched  bar,  which  is  subjected  to  a  number 
of  blows  from  a  falling  weight  until  it  is  fractured  across  the 
notched  portion.  Either  the  number  of  blows  or  the  quantity 
of  energy  absorbed  in  effecting  the  fracture  may  be  taken  as 


266  IEON  AND   STEEL. 

the  measure  of  resistance  to  fracture.  This  method  is  used 
in  at  least  one  large  engineering  works. 

An  important  form  of  apparatus  for  dynamic  testing  is 
shown  in  Fig.  64.  It  may  be  described  as  the  pendulum 
hammer  test.  The  test  piece  is  a  small  bar  2  inches  long, 
§  inch  wide,  and  -f^  inch  thick.  A'notchO'05  inch  deep  is 
cut  across  the  broad  side  f  inch  from  one  end,  and  leaving 
a  thickness  of  0*137  inch  behind  the  notch.  This  test 
piece  is  fixed  upright  in  the  bottom  plate  of  the  machine, 
and  the  pendulum  raised  to  a  given  height.  It  is  then 
allowed  to  fall,  when  a  projection  on  it  strikes  the  test  piece 
and  fractures  it  at  one  blow.  The  pendulum  swings  past 
the  vertical  position,  and  the  distance  to  which  it  rises  011 
the  other  side  is  indicated  by  a  pointer.  The  height  to  which 
it  rises  evidently  depends  upon  the  quantity  of  energy 
absorbed  in  breaking  the  test  piece.  Thus  the  more  the 
kinetic  energy  of  the  falling  weight  is  absorbed  in  the  work 
of  breaking  the  bar  the  smaller  will  be  the  height  to 
which  it  will  rise  after  doing  this  work.  A  measure  of  the 
dynamic  energy  required  to  break  the  bar  is  thus  obtained 
and  comparison  between  different  test  pieces  made. 

Alternating  Stresses. — Simple  bending  backwards  and 
forwards  of  the  test  piece  by  hand  is  a  very  old  method  of 
applying  alternating  stresses,  and  gives  good  results  in 
experienced  hands  ;  but  the  personal  equation  comes  in, 
and  this  is  always  more  or  less  unsatisfactory.  Prof.  Arnold 
has,  however,  developed  a  method  and  constructed  a  machine 
for  carrying  out  alternating  tests  that  is  sure  to  be  largely 
used  in  the  future.  The  test  bar,  which  is  f  inch  square  and 
several  inches  long,  is  fixed  in  a  die  in  a  vertical  position,  so 
that  a  length  4  inches  is  left  free.  The  free  end  is  then 
bent  rapidly  backwards  and  forwards  by  means  of  an 
eccentric  geared  to  a  vertical  shaft.  In  this  way  a  large 
number  of  pushes  and  pulls  per  minute  can  be  given  to  the 
bar.  Also  the  rate  and  magnitude  of  these  alternating 


MECHANICAL   PEOPEETIES  OF   IEON   AND   STEEL.     267 

stresses  can  be  varied  to  suit  the  particular  test.  The 
average  stress  is  a  little  above  the  elastic  limit  of  the  test 
bar,  and  so  determines  its  fracture  in  a  reasonable  time. 
Prof.  Arnold  gives  as  an  illustration  the  case  of  good  boiler 
plate  steel,  which,  when  under  these  alternating  stresses  at 
the  rate  of  166  per  minute,  broke  after  1,375  alternations. 
On  increasing  the  rate  to  266  per  minute  a  similar  bar  of 
the  same  steel  broke  after  878  alternations.  Thus  the 
resistance  diminishes  as  the  rate  increases,  and  this  shows 
that  care  is  required  in  the  selection  of  materials  for  the 
construction  of  high  speed  engines.  Captain  Sankey  gives 
an  example  of  a  test  bar  of  chromium  vanadium  steel 
tested  by  Arnold  that  endured  1,206  alternations  at  the  rate 
of  710  per  minute.  The  motion  of  the  free  end  of  the  bar 
on  each  side  of  the  vertical  line  is  f  inch.  The  test  appears 
to  be  a  most  important  one  in  the  selection  of  material,  and 
is  sure  to  be  developed  to  its  full  extent  in  the  able  hands 
of  its  inventor.  Another  method  of  applying  these  transverse 
stresses  is  by  hanging  a  weight  at  the  free  end  of  a  bar, 
and  then  causing  the  bar  to  rotate  rapidly.  The  test  bar, 
which  has  a  shallow  groove  turned  in  it,  is  fixed  in  a  chock 
that  can  be  driven  by  a  pulley,  the  number  of  revolutions 
of  which  is  counted  by  a  registering  apparatus  attached  to 
it.  The  free  end  of  the  bar  is  fitted  with  a  small  pulley, 
over  which  a  flexible  cord  passes.  One  end  of  this  cord  is 
fastened  to  the  floor  a  little  out  of  the  vertical  line  passing 
through  the  pulley,  and  the  other  end  is  attached  to  a 
weight  which  thus  hangs  from  the  pulley,  and  exerts  a  steady 
pressure  upon  the  bar  to  which  the  pulley  is  fastened.  This 
pressure  may  be  regarded  as  acting  along  a  vertical  diameter 
of  a  given  cross-section  of  the  bar,  and  as  this  diameter  is 
reversed  in  every  revolution  of  the  bar,  the  pressure  alternates 
in  direction  with  respect  to  the  moving  bar.  The  stresses 
here  are  comparatively  small  and  well  within  the  elastic 
limit.  This  method  has  been  developed  by  Mr.  J.  E.  Stead. 


CHAPTEK  XI. 

IRON    AND    STEEL    UNDER    THE    MICROSCOPE. 

PURE  iron,  in  common  with  other  metals,  has  a  crystalline 
structure,  and  this  is  shown  very  clearly  when  a  small 
sample  of  the  metal  is  properly  prepared  and  examined 
under  the  microscope.  Iron  crystals  of  considerable  size 
have  been  observed  from  time  to  time,  but  they  are  only 
formed  under  exceptional  circumstances,  and  for  general 
observation  the  microscope  must  be  used.  Crystalline 
bodies  are  very  common  among  the  solids  of  the  mineral 
kingdom,  and  have  taken  on  their  crystalline  character 
while  passing  from  the  liquid  into  the  solid  state.  Such 
bodies  may  have  been  in  solution  in  water,  or  other  solvent, 
from  which  they  have  crystallised,  the  solvent  remaining 
in  the  liquid  state  after  the  separation  of  the  solid ;  or 
they  may  have  been  in  solution  in  molten  solid  matter, 
and  then  crystallised  out  during  the  extremely  slow  cooling 
and  solidification  of  the  whole  mass ;  or,  if  pure  substances, 
they  may  have  crystallised  on  solidification.  An  isolated 
crystal  has  a  definite  geometrical  form  which  is  easily 
recognised  by  the  crystallographer ;  but  when  a  molten 
mass  crystallises  on  solidification  the  individual  crystals 
interfere  with  each  other,  and  it  is  often  difficult  to 
recognise  the  particular  form  of  the  crystals,  although  the 
crystalline  character  of  the  whole  may  be  evident.  When 
the  crystals  are  microscopic  they  are  usually  spoken  of  as 
"  crystal  grains,"  and  the  fractured  surface  of  a  piece  of 
metal  made  up  of  these  minute  crystals  presents  a  finely 
granular  appearance. 


IEON  AND  STEEL   UNDER  THE  MICROSCOPE.       269 

Some  of  the  commercial  irons  show  the  crystalline 
structure  very  markedly,  but  this  evident  crystallisation  is 
usually  caused  by  the  presence  of  other  elements,  and  to  the 
treatment  the  metal  has  undergone.  The  constituents  of 
the  different  varieties  of  iron  are  often  spoken  of,  and  they 
have  now  to  be  considered ;  but  it  is  well  to  remember  in 
approaching  this  subject  that  pure  iron  has  only  one 
constituent,  and  to  that  the  name  "  Ferrite  "  has  been 
given.  This  constituent  is  crystalline  when  solid,  so  that 
if  a  mass  of  pure  iron  in  the  molten  state  is  allowed  to 
solidify,  it  crystallises  as  it  becomes  solid,  and  when  the 
solidification  is  allowed  to  take  place  under  given  conditions 
the  crystals  are  always  the  same.  The  size  of  the  crystals 
will  vary,  but  this  is  simply  a  matter  of  detail. 

The  preparation  of  perfectly  pure  iron  is  a  most  difficult, 
if  not  impossible,  task ;  but  a  specimen  of  the  metal  with 
so  little  impurity  in  it  that  its  presence  cannot  be  detected 
under  the  microscope  can  be  prepared,  and  it  is  upon  the 
examination  of  such  specimens  that  general  statements  are 
based.  The  limits  of  this  book  will  not  allow  of  a  detailed 
account  of  this  very  interesting  subject,  but  it  is  hoped  that 
sufficient  may  be  given  to  render  it  intelligible.  The 
method  is  applicable  to  the  examination  of  any  specimen 
of  iron,  whatever  the  treatment  it  has  undergone,  provided 
it  is  large  enough  to  handle  for  preparation. 

Preparing  the  Specimen. — The  piece  to  be  examined  should 
be  of  convenient  size  to  hold  in  the  fingers.  If  it  is  soft 
enough,  it  is  filed  flat  and  smoothed  on  the  side  to  be 
examined.  It  is  then  rubbed  on  emery  cloth  carefully 
glued  on  a  smooth  plane  surface  of  hard  wood.  A  con- 
venient number  of  these  emery  blocks  is  six,  ranging  from 
F  to  0000,  but  they  need  not  all  be  used  for  one  specimen. 
The  filed  surface  of  the  specimen  is  rubbed  in  one  direction 
over  the  coarsest  block  until  the  surface  looks  uniform ;  it 
is  then  rubbed  at  right  angles  to  the  former  direction  on 


270  IEON  AND   STEEL. 

the  second  block  until  it  again  looks  uniform.  This  is 
repeated  on  the  other  blocks,  starting  at  right  angles  to  the 
last  direction,  until  the  finest  has  been  used.  A  pocket 
lens  is  useful  for  examining  the  specimen  during  the  rubbing 
down  process.  The  surface  has  then  to  be  polished  and 
freed  from  microscopic  scratches  by  rubbing  it  on  a  rouge 
pad,  which  consists  of  a  piece  of  good  chamois  leather 
stretched  on  a  flat  surface.  The  rouge  must  be  of  the 
finest  if  a  perfectly  polished  specimen  is  to  be  obtained. 
A  well  prepared  surface  has  a  smooth,  bright,  uniform 
appearance  when  looked  at  under  the  microscope.  It  is 
quite  free  from  scratches,  and  generally  shows  no  signs  of 
structure,  but  sometimes  the  polishing  may  bring  out 
certain  structures  which  become  evident  under  the  micro- 
scope. This  is  so  when  the  constituents  differ  in  hardness. 
The  softer  portions  of  the  surface  are  more  rubbed  away 
than  the  harder  ones,  and  this  is  accentuated  by  the  use  of 
a  yielding  polishing  surface. 

For  research  work,  in  order  that  false  impressions  may 
be  avoided,  very  great  care  must  be  taken  in  the  prepara- 
tion of  the  polished  surface,  and  elaborate  descriptions  of  this 
preparation  are  given  in  original  papers  and  works  on  the 
subject.  But  for  the  recognition  of  well-known  constituents 
by  the  expert  in  the  works  laboratory,  such  fine  work  is  not 
necessary,  and  the  preparation  already  described  is  ample. 
The  labour,  however,  is  much  lightened  by  the  use  of 
polishing  machines.  In  most  of  these  the  polishing  disc 
is  screwed  on  to  a  vertical  spindle  so  that  it  can  be  rotated 
rapidly  in  a  horizontal  plane  at,  say,  about  2,000  revolutions 
per  minute.  For  polishing  with  rouge  a  piece  of  fine  cloth 
is  stretched  over  the  disc,  and  held  in  position  by  a  metal 
ring,  which  is  forced  over  the  circumference  of  the  disc  like 
the  tyre  of  a  wheel.  The  cloth  is  slightly  wetted,  the  rouge 
applied,  and  the  polishing  effected  by  pressing  the  specimen 
on  the  revolving  surface. 


IRON  AND  STEEL  UNDER  THE  MICROSCOPE.       271 

A  tin  disc,  or  "  lap,"  revolving  in  a  horizontal  plane,  and 
fed  with  a  thin  paste  of  emery  and  water,  is  very  useful  for 
grinding  down  hard  specimens  that  cannot  he  filed  flat. 
The  usual  preparation  then  follows. 

Etching. — The  next  process  is  the  etching  of  the  surface 
with  some  corrosive  liquid,  and  this  requires  some  care  and 
considerable  experience  to  do  satisfactorily ;  but  the  principle 
upon  which  it  depends  is  very  simple.  Now,  suppose  the 
surface  to  be  perfectly  uniform,  both  chemically  and 
physically,  then,  if  it  were  immersed  in  any  solvent  liquid, 
the  surface  would  be  dissolved  away  equally  all  over  ;  but 
if  the  surface  is  not  uniform,  either  physically  or  chemically, 
and  few  surfaces  are,  then  the  solvent  liquid  will  act  more 
rapidly  on  some  parts  than  on  others,  and  the  structure 
will  be  brought  out.  The  chief  thing  in  etching  is  to  stop 
the  action  of  the  solvent  liquid  as  soon  as  the  structure  is 
sufficiently  developed,  and  this  is  largely  a  matter  of 
experience. 

The  following  are  the  common  etching  solutions:  — 

(1)  A  10  per  cent,  solution  of  iodine  in  alcohol. 

(2)  A  5  per  cent,  solution  of  picric  acid  in  alcohol. 

(3)  A  2  per  cent,  solution  of  nitric  acid  in  water. 

(4)  A    1    per    cent,    solution    of    hydrochloric    acid    in 
alcohol. 

(5)  A    2   per    cent,    solution    of   ammonium   nitrate    in 
water. 

(6)  An  infusion  of  liquorice  root  in  water. 

(1)  and  (2)  are  largely  used  for  cast  irons,  and  (3)  for 
steels.  A  much  stronger  solution  of  nitric  acid  than  (3)  is 
sometimes  used. 

Before  etching,  the  surface  is  examined  to  see  that  it  is 
free  from  grease  and  finger  marks.  If  the  tincture  of 
iodine  is  used,  a  drop  is  put  on  the  surface  to  be  etched  and 
rubbed  over  it  with  the  finger  tip.  This  is  repeated  until 


272  IEON  AND   STEEL. 

the  structure  is  brought  out.  The  surface  is  then  washed 
with  alcohol  and  dried. 

When  an  acid  is  used,  the  metal  is  immersed  in  the 
solution  contained  in  a  porcelain  or  glass  dish.  As  the 
action  proceeds,  the  surface  is  watched  through  a  pocket 
lens,  and  when  it  is  judged  to  have  gone  far  enough  the 
piece  is  removed,  well  swilled  with  water,  immersed  in 
alcohol,  and  dried.  The  surface  is  passed  lightly  pver  the 
rouge  pad,  or  a  similar  pad  free  from  rouge,  and  is  then 
ready  for  mounting.  The  simplest  method  of  mounting  is 
to  put  a  metal  ring  over  the  specimen  as  it  lies  on  the 
rouge  pad,  and  to  press  upon  its  upper  surface  a  cover  glass, 
on  which  a  piece  of  plasticene  has  been  stuck.  If  the 
cover  glass  is  pressed  down  until  it  is  stopped  by  the  ring, 
the  metal  adheres  to  the  plasticene,  and  when  the  glass  is 
lifted  away  comes  away  with  it.  The  prepared  surface  is 
parallel  with  the  surface  of  the  glass,  and  the  mounted 
specimen  is  ready  to  be  placed  on  the  stage  of  the  micro- 
scope. The  etching  may  have  to  be  repeated  one  or  more 
times  to  bring  out  the  structure  properly. 

Liquorice  root  and  ammonium  nitrate  solutions  are 
usually  put  on  to  a  piece  of  parchment  stretched  on  a  plate 
of  glass.  The  polished  specimen  is  then  rubbed  on  the 
moistened  parchment  until  the  required  effect  is  produced. 
Ammonium  nitrate  is  the  more  effective  of  these  two  reagents. 

A  rapid  method  for  works  practice  is  described  by 
Professor  Arnold.  The  sample  is  filed  or  ground  flat  and 
rubbed  down  on  the  0  and  00  emery  blocks;  it  is  then 
immersed  in  nitric  acid  solution  of  sp.  gr.  1*2  for  about  a 
minute,  or  until  a  black  film  appears  on  the  surface,  and 
bubbles  of  gas  are  about  to  escape.  The  metal  is  then 
removed,  swilled,  dried,  and  mounted  for  the  microscope. 
Any  scratches  left  in  from  the  rubbing  down  are  largely 
removed  by  the  acid,  and  the  structure  is  well  defined.  It 
is  suitable  for  the  rapid  examination  of  many  steels. 


IRON  AND  STEEL  UNDER  THE  MICROSCOPE.       273 

Another  way  of  bringing  out  the  structure  is  known  as 
"heat  tinting."  The  polished  specimen  is  put  on  a  hot 
iron  plate,  watched  till  the  colours  appear,  and  then  plunged 
into  mercury.  In  this  way  the  different  constituents  often 
take  on  different  colours.  Some  of  the  reagents  themselves 
often  impart  colour  to  one  or  more  of  the  constituents  in 
the  structure  of  the  etched  surface. 

The  Microscope. — The  specimen  is  now  ready  for 
examination  under  the  microscope,  and  a  short  description  of 
this  instrument  may  be  useful.  It  is  well  known  that  a  piece 
of  curved  glass,  or  "  lens,"  as  it  is  called,  will  magnify  a  body 
which  is  looked  at  through  it.  The  magnified  appearance 
as  seen  by  the  eye  is  simply  an  enlarged  image  of  the 
object  formed  by  the  lens.  With  an  ordinary  pocket  lens 
the  image  is  on  the  same  side  of  the  lens  as  the  object,  and 
is  a  virtual  image,  but  this  depends  upon  the  position  of  the 
object  with  respect  to  the  focus  of  the  lens  ;  if  it  is  outside 
the  focus  a  real  image  is  formed  in  the  space  on  the  other 
side  of  the  lens.  In  the  compound  microscope  an  arrange- 
ment of  lenses  which  acts  as  nearly  as  possible  like  a 
perfect  single  lens,  and  known  as  the  objective,  is  used  to 
obtain  a  magnified  real  image  of  an  object  placed  behind  it, 
and  just  outside  the  focus.  This  image  is  then  looked  at  by 
another  combination  of  lenses,  the  eye-piece,  which  is  so 
placed  that  the  real  image  formed  by  the  objective  falls 
inside  the  focus  of  the  eye-piece,  and  a  magnified  virtual 
image  of  the  real  image  is  seen  on  looking  through  the  eye- 
piece. Thus,  by  this  combination,  two  magnifications  are 
effected,  and  a  sharp  image  is  obtained  when  the  object,  the 
objective,  and  the  eyepiece  are  in  their  proper  relative 
positions.  The  two  lenses  are  at  the  opposite  ends  of  a 
double  tube,  so  that  the  distance  between  them  can  be 
readily  regulated  by  drawing  out  or  pushing  in  the  tube 
carrying  the  eye-piece.  The  object  is  placed  on  a  stage 
011  which  it  can  be  moved  into  any  required  position,  and 

i.s.  T 


274  IEON  AND   STEEL. 

the  tube  carrying  the  object  glass  can  also  be  moved  to  and 
from  the  object  by  means  of  a  coarse  and  fine  rack  motion, 
the  fine  motion  being  used  for  the  final  adjustment.  The 
microscope,  therefore,  consists  of  a  stand  to  support  the  stage 
on  which  the  object  is  placed,  and  the  tube  carrying  the 
lenses,  together  with  the  necessary  gear  for  getting  the 
object  into  focus. 

An  object,  to  give  a  clear,  well  defined  image,  must  be 
illuminated,  and  this  presents  more  difficulty  in  the  case  of 
opaque  objects  than  it  does  with  transparent  ones.  All 
metal  specimens  are  opaque,  so  that  only  the  following 
mode  of  illumination  need  be  considered. 

The  light  must  be  reflected  from  the  surface  of  the  object 
through  the  objective,  up  the  tube,  and  through  the  eye-piece 
to  the  eye.  Now  when  the  light  is  focussed  on  the  object 
entirely  from  outside,  the  axis  of  the  tube  must  be  inclined 
to  the  surface  of  the  object,  so  that  the  light  striking  the 
surface  may  be  reflected  up  the  tube.  This  is  called 
oblique  illumination,  and  although  sometimes  used,  does  not 
give  much  information.  Vertical  illumination  is  mostly 
used,  and  this  is  best  effected  by  placing  a  right  angled 
glass  prism  inside  the  tube,  and  just  above  the  objective, 
so  that  it  can  be  rotated  opposite  to  a  hole  in  the  side  of 
the  tube.  The  light  from  a  lamp  is  focussed  through  this 
hole  by  a  condensing  lens,  and  is  reflected  downwards 
by  the  oblique  side  of  the  prism.  It  thus  falls  on  the  surface 
of  the  specimen,  which  then  reflects  it  back  through  the 
objective,  behind  the  prism,  and  to  the  eye-piece ;  so  that 
the  image  is  formed  by  light  coming  vertically  from  the 
surface  under  examination,  and  no  distortion  is  caused. 

The  object  lenses  are  in  a  small  case  which  can  be 
screwed  on  and  off  the  end  of  the  microscope  tube.  The 
prism  also  is  often  fitted  in  a  case  which  can  be  screwed 
into  the  tube  before  the  objective  is  put  in.  There  are 
usually  several  objectives  of  different  focal  lengths.  The 


IRON  AND   STEEL   UNDER  THE   MICROSCOPE.       275 

most  useful  are  the  J  inch,  ^  inch,  and  the  1  inch.  The 
shorter  the  focal  length  the  greater  the  magnifying  power 
of  the  objective  ;  but  the  actual  magnification  depends  also 
on  the  character  and  position  of  the  eye-piece.  The 
magnification  is  usually  expressed  in  linear  dimensions  as 
so  many  diameters.  The  most  useful  magnifications  are 
from  50  to  500.  The  limit  is  about  2,000  diameters. 

By  arranging  a  camera  in  the  place  of  the  eye-piece  the 
image  of  the  section  under  the  microscope  can  be  projected 
on  to  a  photographic  plate,  and  a  photograph  of  it  taken, 
developed,  and  printed  in  the  usual  manner.  The  figures 
which  follow  have  been  produced  in 
this  way. 

The  Constituents  of  Iron  and  Steel. 
—As  already  stated,  the  commercial 
varieties  of  iron  contain  a  number  of 
other  elements  in  various  propor- 
tions, and  the  varying  properties  of 
different  forms  of  the  metal  are  due, 
not  only  to  the  presence  and  pro- 
perties of  these  elements,  but  also  to  FlG  65  _^ 
the  way  in  which  they  are  associated  (Hiorns). 

with  the  iron  and  with  each  other. 

The  association  of  some  of  the  elements  in  a  mass  of 
iron  is  influenced  very  largely  by  the  treatment  the  metal 
has  undergone,  especially  in  heating  and  cooling.  The 
complete  analysis  of  a  sample  can  only  tell  the  actual 
amounts  of  the  various  elements  present,  and  nothing  about 
their  condition,  except  in  case  of  carbon,  when  it  occurs  both 
as  graphite  and  as  combined  carbon.  Of  course,  assumptions 
can  be  made  from  the  known  properties  of  the  elements 
present,  but  they  are  only  assumptions  after  all.  By  the 
use  of  the  microscope,  some  of  these  have  been  found  to  be 
correct,  and  others  fallacious ;  whilst  the  general  view  of 
the  constitution  of  iron  and  steel  has  been  enormously 

T  '2 


276 


IEON  AND  STEEL. 


extended.  Dr.  Sorby,  of  Sheffield  was  the  first  worker  in 
this  field  of  research,  and  published  some  of  the  results  of 
his  labour  as  early  as  1864.  Since  then  many  well-known 
men  have  taken  up  the  work,  and  among  them  may  be 
mentioned  Howe  (America)  ;  Martens  (Germany) ;  Osmond 
(France);  and  Stead  (England). 

Fcrrite. — Now  it  might  be  supposed  that  the  polished 
surface  of  a  piece  of  pure  iron  would  be  perfectly  uniform 
and  continuous,  and  so  it  is  chemically,  consisting  as  it  does 

of  a  single  element ; 
but  it  is  not  so  physi- 
cally, for  the  surface 
cuts  through  crystals, 
the  boundary  planes  of 
which  must  be  re- 
garded as  marking  out 
the  surface  in  the  form 
of  a  network  of  lines. 
The  metal  is  more 
readily  attacked  by  the 
etching  liquid  along 
these  lines  than  in  any 
other  direction,  ac- 
cordingly it  is  more 
eaten  away,  with  the  result  that  when  looked  at  under  the 
microscope  the  lines  are  rendered  visible.  These  lines  on 
the  etched  surface  are  regarded  as  marking  the  boundary 
planes  of  crystals.  Fig.  65  is  the  micrograph  of  a  piece  of 
pure  iron  prepared  by  the  author. 

Cementitc. — This  constituent  is  regarded  as  a  definite 
compound  of  iron  and  carbon,  to  which  has  been  assigned 
the  formula  Fe3C,  as  it  contains  approximately  6'67  per 
cent,  of  carbon.  It  is  very  much  harder  than  ferrite,  more 
difficult  to  scratch,  and  is  attracted  by  a  magnet.  Its  name 
is  derived  from  the  fact  that  it  is  present  in  abundance 


FIG.  66.— Cementite  (Stead). 


IRON  AND   STEEL  UNDER  THE  MICROSCOPE.       277 


in  cemented  bars,  and  the  late  Sir  F.  Abel  obtained  it  as  a 
greyish-black  spangly  mass  by  treating  carefully  annealed 
steel  with  chromic  acid  solution,  which  dissolves  out  the 
ferrite  without  affecting  the  carbide  to  any  great  extent. 
With  other  acid  solvents  the  carbide  is  more  or  less 
decomposed.  Abel  obtained  as  much  as  92'8  per  cent,  of 
the  combined  carbon  of  annealed  steel  in  this  residue.  The 
percentage  of  carbon  was  found  to  vary  from  6*39  to  8'09 
as  compared  with  the  calculated  percentage  of  6'67  ;  but  it 
is  probable  that  the  resi- 
dues were  contaminated 
with  small  quantities  of 
water  and  graphite,  which 
would  account  for  the  varia- 
tions. When  hardened  steel 
was  treated  in  the  same 
way  only  4*7  per  cent,  of 
the  combined  carbon  was 
isolated  as  carbide.  Abel's 
conclusions  have  been  con- 
firmed by  other  workers, 
and  there  is  now  no  doubt 
of  the  existence  of  this 
constituent  of  iron  and  steel.  The  light  portions  in  Fig.  66 
are  patches  of  cementite. 

Pearlite. — This  is  the  most  striking  constituent  of  iron  and 
steel,  and  was  discovered  by  Sorby,  who  gave  it  the  name  of 
the  pearly  constituent  from  its  appearance  under  the 
microscope.  In  its  most  easily  recognised  form  it  consists 
of  alternate  layers  of  cementite  and  ferrite,  which  are  more 
or  less  curved,  and  the  average  thickness  of  a  pair  of  these 
layers  is,  according  to  Stead,  not  more  than  O'OOl  milli- 
metre. This  is  known  as  lamellar  pearlite,  and  is  shown 
in  Fig.  67.  The  black  streaks  are  cementite,  and  the  white 
ones  ferrite.  Sometimes  it  separates  in  granules,  and  is 


FIG.  67.— Pearlite  (Stead). 


278 


IKON  AND   STEEL. 


then  known  as  granular  pearlite.  The  general  appearance 
of  lamellar  pearlite  is  due  to  the  different  degrees  of  hard- 
ness of  the  constituent  layers  causing  the  arrangement  of 
the  layers,  after  polishing  and  etching,  to  resemble  somewhat 
that  of  mother-of-pearl,  and  imparting  to  the  surface  the 
same  play  of  colour,  though  in  a  less  marked  degree.  It  lias 
been  determined  that  pearlite  contains  approximately  O9 
per  cent,  of  carbon ;  so  that  a  steel  of  this  composition, 
when  properly  annealed,  should  be  practically  all  pearlite. 
In  a  steel  containing  less  than  0'9  per  cent,  carbon  the 

excess  of  ferrite  separates 
or  segregates  from  the 
pearlite  ;  but  in  a  steel  con- 
taining more  than  this 
quantity  cementite  segre- 
gates. These  constituents 
are  easily  recognised  in 
sections  containing  them. 

Martensite.  —  This  con- 
stituent is  just  as  well 
defined  under  the  micro- 
scope as  any  of  the  others, 
but  there  is  not  such  a 

general  concensus  of  opinion  of  its  composition  among  the 
various  authorities.  The  simple  view7  is  that  it  is  unsegre- 
gated  pearlite,  that  is,  a  combination  of  iron  and  carbon 
containing  0'9  per  cent,  of  carbon  which  has  crystallised 
without  separating  into  carbide  and  ferrite.  Most  autho- 
rities follow  Osmond  in  regarding  it  as  a  solid  solution 
of  carbon,  or  of  the  carbide,  in  iron  which  crystallises 
as  such.  Arnold,  however,  thinks  that  it  is  an  iron 
sub-carbide  Fe24C.  Martensite  takes  the  form  of  inter- 
lacing needles,  and  is  best  produced  for  recognition  in  steel 
containing  less  than  0'8  per  cent,  carbon,  when  it  is  raised 
to  a  bright  red  heat,  allowed  to  cool  to  a  cherry-red,  and 


FIG.  68. — Austenite  and  Martensite. 


IEON  AND   STEEL   UNDER  THE  MICROSCOPE.       279 

then  suddenly  quenched  in  a  freezing  mixture  of  ice  and 
salt. 

In  the  0'9  per  cent,  carbon  steel  the  martensite  is  known 
as  hardenite.  This  name  was  proposed  by  Howe  for  the 
principal  constituent  of  hardened  steel.  Osmond  regards 
hardenite  as  martensite  saturated  with  carbon. 

In  the  higher  carbon  steels  another  constituent  has 
been  recognised,  and  is  called  aiistenite  ;  it  is  softer 
than  martensite,  and  can  be  scratched  with  a  needle.  It 
separates  from  martensite  when  a  steel  containing  more 
than  1*1  per  cent,  of  carbon  is  raised  above  1,000°C. 
(a  light  yellow  heat),  and  then  quenched  in  ice-cold  water. 
The  structure  is  developed  by  polishing  the  prepared 
specimen  on  parchment,  moistened  with  either  ammonium 
nitrate  solution  or  an  infusion  of  liquorice.  The  austenite 
remains  white  while  the  associated  martensite  turns  brown. 
Fig.  68  shows  both  austenite  and  martensite.  Some 
authorities  do  not  recognise  the  existence  of  austenite, 
and  as  it  has  only  been  observed  in  specimens  submitted  to 
abnormal  treatment,  it  is  not  of  much  importance  to  the 
practical  man.  On  the  other  hand,  martensite  exists  in  all 
steels  at  a  temperature  above  that  at  which  they  are 
hardened  when  quenched. 

If  steel  is  allowed  to  cool  slowly,  the  martensite  under- 
goes transition  into  pearlite,  and  if  during  this  transition 
the  metal  is  quenched  by  plunging  it  into  molten  lead,  its 
microstructure  indicates  that  the  transition  has  been 
arrested,  and  a  permanent  structure  produced.  The  most 
familiar  of  these  transition  forms  is  called  sorbite,  after 
Dr.  Sorby,  and  its  permanent  formation  in  medium  carbon 
steel  has  been  put  to  practical  use,  as  will  be  indicated  later. 
Another,  but  much  more  difficult  transitional  form  to 
obtain,  is  known  as  troostite. 

Graphite. — As  the  content  of  carbon  increases  there  is  a 
tendency  for  some  of  that  element  to  crystallise  from  the 


280 


IEON  AND   STEEL. 


cooling  metal  in  the  elementary  form.  The  slower  the 
cooling  through  a  particular  range  of  temperature,  the 
greater  the  tendency  of  the  carbon  to  crystallise  as 
graphite.  The  metal  in  which  graphite  is  best  observed  is 
grey  pig  iron  ;  and  it  is  considered  that  the  presence  of 
silicon  in  the  commercial  metal  is  largely  responsible  for 
the  formation  of  graphite  under  the  normal  conditions  of 
cooling  of  the  pig  metal  in  the  beds.  Mr.  A.  H.  Hiorns 
has  shown  that  graphite  separates  from  iron  containing 


FIG.  69. — Graphite  and  Fertile. 

very  little  silicon  by  keeping  it  above  1,000°C.  for  several 
hours.  Fig.  69  shows  the  graphite  plates  obtruding  among 
the  crystal  grains  of  ferrite  in  the  micro  section  of  a  grey 
pig  iron. 

Generally  speaking,  as  the  grade  number  of  the  pig  iron 
increases,  the  size  of  the  graphite  plates  decreases ;  in  the 
mottled  variety  it  is  somewhat  scanty,  and  the  plates  small. 
In  white  iron  the  graphite  is  practically  absent.  Graphite 
is  not  usually  met  with  in  steel ;  but  the  micrograph  of  a 
high  carbon  steel,  kept  for  some  time  at  a  temperature 


IRON  AND  STEEL   UNDER  THE  MICROSCOPE.      281 


within  the  graphite  forming  range,  shows  evidence  of  its 
separation. 

All  the  variations  in  structure  which  have  been  described 
so  far,  can  be  produced  in  alloys  of  iron  with  varying  pro- 
portions of  carbon  by  suitable  heat  treatment ;  but  the  other 
elements,  silicon,  manganese,  sulphur,  and  phosphorus, 
when  they  are  present  exert  a  considerable  influence  on  the 
structure  of  the  metal.  This  is  most  marked  in  the  case  of 
cast  iron,  for  the  quantities  present  in  wrought  iron  and 
steel  are  usually  small, 
except  manganese,  which 
is  often  present  in  ingot 
iron  and  steel,  and  acts 
as  a  corrective. 

Silicon  unites  with 
iron  to  form  silicides,  of 
which  there  appear  to 
be  two,  FeaSi  in  low 
silicon,  and  FeSi  in  high 
silicon  metal.  The  pre- 
sence of  silicon  can  only 
be  detected  in  ferro- 
silicon.  In  cast  iron  it 
probably  remains  in  the 
solid  solution  or  struc- 
tureless matrix  from  which  the  graphite  has  been  rejected. 
According  to  Heyn,  silicon  lowers  the  range  of  temperature 
within  which  the  graphite  can  separate,  and  thus  facilitates 
its  separation  under  normal  conditions  of  cooling. 

Manganese  acts  against  the  separation  of  graphite,  and 
this  is  probably  due  to  complex  causes,  for  manganese 
combines  with  both  carbon  and  silicon  to  form  fairly  stable 
compounds. 

Sulphur  unites  with  iron  to  form  ferrous  sulphide,  FeS, 
but  \vhen  manganese  is  present  the  sulphur  appears  to 


FIG.    70. — Cast    Iron    containing 
Sulphur. 


282 


IRON  AND   STEEL. 


combine  with  it,  and  the  influence  of  the  separate  elements 
is  largely  counteracted.  Sulphide  of  manganese  crystals 
are  sometimes  plainly  discernible  in  the  micro  sections  of 
cast  irons.  Manganese  is  usually  regarded  as  an  antidote 
for  sulphur,  and  it  is  certain  that  the  bad  effects  of  the  latter 
element  on  the  working  properties  of  the  iron  are  not 
nearly  so  marked  in  the  presence  of  manganese. 

The  general  effect  of  sulphur  on  cast  iron  is  to  harden 
it  and  render  it  brittle.     There  should  not  be  more  than 

0*2  per  cent,  present, 
and,  if  possible,  the 
amount  should  be  less 
than  0'  L  per  cent.  Fig. 
70  show's  the  rnicrostruc- 
ture  of  a  white  cast  iron 
containing  0'2  per  cent, 
of  sulphur.  The  dark 
patches  are  pearlite,  and 
the  light  ones  cementite, 
in  which  the  sulphide  is 
imbedded. 

Phosphorus  unites 
with  iron  to  form  a 
fairly  stable  phosphide 
of  the  metal  having  the 
composition  Fe3P.  The  general  effect  of  phosphorus  in 
wrought  iron  and  steel  is  to  render  the  metals  "  cold  short." 
In  cast  iron  the  presence  of  the  element  lowrers  the  melting- 
point,  and  makes  the  metal  more  fluid  when  melted.  It 
thus  enables  the  molten  metal  to  take  the  impression  of  the 
mould  more  readily,  and  produce  finer  castings.  At  the 
same  time  it  reduces  the  strength  of  the  castings,  so  that 
the  percentage  of  phosphorus  present  must  be  carefully 
regulated  according  to  the  purpose  for  which  they  are  to 
be  used.  The  iron  phosphide  forms  a  eutectic  which  is 


FIG.   71.— Cast   Iron  with   Phosphide 
Eutectic. 


IEON  AND    STEEL  UNDER   THE  MICROSCOPE.       283 

distributed  in  patches  through  the  structure  of  the  metal. 
Fig.  71  is  the  micro  section  of  phosphoric  pig  iron,  con- 
taining 1'5  per  cent,  of  phosphorus,  in  which  the  phosphorus 


Annealed. 


FJG.  72. 


Hardened. 


eutectic  appears  as  small  dark  marks  in  the  irregular 
patches  of  lighter  cementite. 

Copper  and  arsenic  are  found  in  some  varieties  of  iron 
and  steel,  but  their  influence  on  the  structure  and  properties 
of  the  metals  is  not  very  marked,  on  account  of  the 
smalmess  of  the  quantities  usually  present. 

Fig.  72  shows  clearly  the  great  difference  in  the  structure 
of  the  same  steel  (a)  when  carefully  annealed,  and  (b)  when 
quenched  in  cold  water  from  about  800°  C.  The  samples 
from  which  the  specimens  were  cut  contained  0*9  per  cent, 
of  carbon,  and  had  been  subjected  to  a  very  careful  and 
prolonged  annealing.  The  hardened  specimen  was  heated 
in  a  muffle,  and  plunged  into  cold  water. 


CHAPTER  XII. 

HEAT    TREATMENT    OF    IRON    AND    STEEL. 

IN  dealing  with  the  complex  changes  that  take  place  when 
pieces  of  iron  and  steel  are  subjected  to  the  action  of  heat, 
it  would  be  well  to  keep  in  mind  the  kind  of  material  to  be 
dealt  with.  The  generalisation  proposed  by  Professor  Howe 
is  the  best  for  this  purpose.  He  regards  all  the  varieties 
of  commercial  iron  as  more  or  less  impure  steels,  or  alloys 
of  iron  and  carbon.  As  already  stated,  the  normal  con- 
stituents of  annealed  steel  are  pearlite,  ferrite,  and  cementite. 
Thus  the  softest  and  purest  Swedish  bar  iron  would  consist 
almost  entirely  of  ferrite  with  a  little  pearlite.  Then,  as 
the  percentage  of  carbon  increased  the  ferrite  would  be 
more  and  more  replaced  by  pearlite  until  with  0'9  per  cent, 
of  carbon  the  whole  mass  would  consist  of  pearlite.  With 
further  increase  of  carbon  the  pearlite  would  be  partially 
replaced  by  cementite,  and  this  would  continue  until  about 
2  per  cent,  of  carbon  is  reached,  and  the  steel  becomes  white 
cast  iron.  This  generalisation  is  borne  out  by  the  fact  that 
the  difference  between  steel  and  white  cast  iron  is  only  one 
of  degree.  The  mottled  iron  may  be  regarded  as  consisting 
of  a  matrix  of  steel  with  graphite  scattered  through  it ;  and 
the  grey  iron  as  mild  steel  with  graphite  distributed  in  the 
same  manner,  with  variations  in  structure  produced  by 
silicon,  manganese,  phosphorus,  and  sulphur  considered  as 
impurities. 

The  ultimate  effect  of  heat  upon  iron  is  to  convert  it  into 
vapour,  but  an  exceedingly  high  temperature  is  necessary 
for  the  rapid  vaporisation  of  the  metal.  The  range  of 


HEAT  TREATMENT   OF   IRON   AND   STEEL. 


1800 


zing  Point  of  Pure  Iron 


temperatures  usually  considered  lie  between  the  temperature 
of  the  atmosphere,  and  the  melting  point  of  the  metal,  a 
range  of  about  1,600°  C.  But  Moissan  has  experimented 
with  iron  at  the  exceedingly  high  temperature  of  the  electric 
arc,  and  Dewar  at  the  exceedingly  low  temperature  produced 
by  liquid  air. 

The  general  method  of  finding  the  effect  of  heat  on  a 
solid  is  to  melt  it,  and  then  note  the  changes  which  take 
place  as  the  liquid  cools,  solidifies,  and  finally  cools  down 
to  the  original  temperature  of 
the  solid.  The  usual  way  of 
doing  this  is  to  put  a  thermo- 
meter (or  pyrometer  for  very 
high  temperatures)  into  the 
liquid,  and  note  the  rate  of  fall 
in  temperature.  The  cause  of 
the  fall  in  temperature  is  the 
escape  of  heat  from  the  body 
into  the  surrounding  space,  and 
if  no  internal  change  other  than 
the  escape  of  heat  takes  place 
this  will  follow  a  regular  law. 
The  simple  way  of  recording 
the  outward  flow  of  heat  is  to 
note  the  temperatures  at  equal 
intervals  of  time,  and  record  them  on  a  curve  diagram. 
Take  the  case  of  pure  molten  copper:  the  fall  in  tempera- 
ture is  represented  by  a  regular  curve  until  the  metal 
begins  to  solidify,  when  the  fall  is  arrested,  but  as  the  time 
still  goes  on  this  portion  of  the  curve  becomes  a  horizontal 
line.  The  reason  for  this  is  well  known,  for  when  a  solid 
liquefies  heat  disappears  as  such  in  effecting  the  physical 
change  from  solid  to  liquid.  When  the  liquid  solidifies 
again  the  heat  of  liquefaction  appears  at  the  same  rate  as 
heat  is  radiated  from  the  cooling  body,  so  that  the  internal 


600 


Time. 

FIG.  73. 


286  IRON  AND   STEEL. 

temperature  does  not  fall  as  long  as  any  of  the  body 
remains  liquid.  When  the  copper  has  solidified  the  fall 
in  temperature  is  again  represented  by  a  regular  down- 
ward curve.  See  Fig.  73. 

In  the  case  of  pure  iron  the  same  is  exactly  true  down  to 
the  freezing  point,  but  the  downward  curve  is  not  regular, 
for  an  arrest  takes  place  at  890°  C.,  and  still  another  at 
750°  C.,  when  the  curve  becomes  slightly  horizontal.  These 
points  are  denoted  by  the  symbols  Ar3  and  Ar2,  and  their 
existence  shows  clearly  that  an  internal  change  of  some 
kind  takes  place  by  which  sufficient  heat  is  developed  to 
counterbalance  that  given  out  by  the  cooling  metal.  When 
the  Ar2  point  is  passed  the  cooling  curve  becomes  regular 
again,  and  keeps  so  down  to  the  temperature  of  the 
atmosphere.  An  explanation  of  this  difference  between 
iron  and  copper  was  naturally  sought  for.  Now,  if  iron  be 
regarded  as  an  element  with  its  atoms  all  alike,  these 
evolutions  of  heat  must  be  accompanied  by  some  rearrange- 
ment of  the  atoms  in  the  molecules  themselves,  by  which 
the  quantity  of  energy  associated  with  them  is  diminished 
to  the  exact  amount  of  the  heat  liberated. 

Allotropy. — There  are  several  elements  that  can  exist  in 
different  forms  at  the  same  temperature,  and  it  is  well 
known  that  different  quantities  of  energy  are  associated 
with  them.  These  are  called  allotropic  modifications  of  the 
elements.  Carbon  is  the  well-known  example  in  its  three 
forms,  the  Diamond,  Graphite,  and  Charcoal.  A  given 
weight  of  each  of  these  bodies  when  completely  burnt 
furnishes  exactly  the  same  weight  of  carbon  dioxide ;  but 
the  quantity  of  heat  developed  is  not  the  same.  This  shows 
conclusively  that  the  three  bodies  are  one  and  the  same 
chemical  element,  but  that  the  internal  arrangement  of  the 
atoms  and  molecules  and  energy  associated  with  them  are 
not  the  same,  and  it  is  to  this  that  the  marked  variations 
in  properties  are  due.  These  forms  of  carbon  exist  through 


HEAT  TREATMENT   OF   IRON  AND   STEEL.          287 

a  wide  range  of  temperature,  and  are  therefore  popularly 
regarded  as  stable  bodies.  But  even  the  diamond  is 
changed  into  a  mass  of  black  charcoal  when  rapidly  heated 
to  the  temperature  of  the  electric  arc. 

Sulphur  furnishes  another  example.  This  element  can 
exist  in  three  distinct  allotropic  states  ;  but  the  tempera- 
ture range  is  much  smaller  than  in  the  case  of  carbon. 
There  are  two  well-known  crystalline  forms,  one  of  which, 
the  monoclinic,  is  stable  above  96°  C.,  and  the  other,  the 
rhombohedral,  below  that  temperature.  The  latter  is  the 
stable  form  at  ordinary  temperatures,  and  well  denned 
crystals  can  be  obtained  from  a  solution  of  sulphur  in 
carbon  bisulphide  ;  but  when  the  solid  is  melted  (114'5°  C.) 
and  then  slowly  cooled  monoclinic  crystals  are  formed.  Also 
when  the  liquid  is  heated  above  250°  C.  and  then  suddenly 
cooled  by  being  poured  into  cold  water,  a  plastic  form  of  the 
element  is  obtained.  Both  these  pass  back  to  the  stable 
form  with  evolution  of  heat,  if  left  to  themselves  at  the 
temperature  of  the  air,  for  they  are  below  their  transition 
pointy  as  the  lowest  temperature  at  which  they  are  stable  is 
called.  But  there  is  a  considerable  amount  of  reluctance 
or  lag  about  this  change,  which  is  due  to  some  kind  of 
molecular  inertia.  The  form  tends  to  persist  below  its 
transition  point,  and  is  then  said  to  be  in  the  metastable 
condition.  Tin  furnishes  a  good  example  of  this.  The 
transition  point  of  ordinary  tin  is  20°  C.,  so  that  it  is  in  the 
metastable  condition  except  in  very  hot  weather  ;  but  its 
passage  to  the  stable  form,  a  grey  powder,  is  excessively 
slow  under  normal  conditions,  although  when  subjected  to 
great  cold  it  may  be  effected  in  a  few  months.  Thus  blocks 
of  tin  have  been  known  to  crumble  to  powder  when  exposed 
to  the  rigour  of  a  severe  Russian  winter. 

With  these  well-known  cases  in  view  it  is  not  at  all 
difficult  to  accept  the  conclusion  of  Osmond,  that  iron  can 
exist  in  different  allotropic  states  within  certain  ranges  of 


288  IEON  AND   STEEL. 

temperature ;  and  just  as  we  speak  of  diamond-carbon, 
graphitic-carbon,  and  amorphous-carbon  he  speaks  of 
alpha-iron,  beta-iron,  and  gamma-iron,  using  the  names  of 
the  first  letters  of  the  Greek  alphabet  a,  ,3,  y,  to  distin- 
guish the  different  forms.  Now  a- iron  is  the  normal  form, 
and  exists  below  750°  C. ;  /3-iron  exists  in  the  range  between 
750°  C.  and  890°  C. ;  and  y-iron  above  890°  C.  These  different 
forms  of  the  metal  have  different  physical  and  mechanical 
properties.  Thus  alpha-iron  is  soft  and  magnetic  ;  beta- 
iron  is  hard  and  non-magnetic  ;  gamma-iron  is  non-magnetic 
and  soft.  Now  it  may  be  remarked  that  although  this 
allotropic  theory  for  iron  is  not  universally  accepted,  general 
opinion  is  strong  in  its  favour,  and  it  certainly  gives  a 
simple  explanation  of  observed  facts. 

But  when  carbon  is  associated  with  the  iron  these 
changes  are  considerably  modified,  and  with  about  0'6  per 
cent,  present  the  points  Ar3  and  Ar2  are  both  lowered,  and 
appear  to  run  together  at  720°  C.  with  a  marked  evolution 
of  heat.  Then,  when  the  temperature  reaches  660°  C.  a 
very  marked  evolution  of  heat  takes  place,  and  the  cooling 
metal  glows  again  with  the  added  heat.  This  change  has 
long  been  known  by  the  name  of  recalescence,  although  its 
cause  was  not  properly  understood. 

Eutectics. — Now  in  order  to  understand  this  important 
phenomenon  it  will  be  necessary  to  consider  the  cooling 
curve  of  an  alloy  such  as  plumber's  solder,  which  consists 
of  two  parts  of  lead  and  one  part  of  tin.  At  a  temperature 
about  the  melting  point  of  lead  it  is  perfectly  fluid,  and  if 
it  is  allowed  to  cool  begins  to  solidify  at  about  240°  C.,  but 
the  temperature  continues  to  fall  through  a  range  of  some 
60°C.  before  complete  solidification  takes  place.  The  freezing 
mass  thus  assumes  a  pasty  condition,  which  enables  a 
skilful  workman  to  work  it  round  the  junction  of  two  pieces 
of  lead  pipe  in  the  process  of  "  wiping  "  a  joint.  A  simple 
explanation  of  this  may  be  given.  When  solidification 


HEAT  TREATMENT   OF   IRON   AND   STEEL. 


first  sets  in  it  is  pure  lead  that  crystallises,  and  this 
crystallisation  proceeds  until  an  alloy  of  approximately  two 
parts  tin  and  one  part  lead  is  left  in  the  liquid  state.  This 
then  solidifies  at  180°  C.,  and  the  whole  mass  becomes  solid. 
The  pasty  material  with  which  the  plumber  works,  consists 
of  small  crystals  of  solid  lead  wetted  by  the  molten  alloy  of 
lead  and  tin.  The  alloy  containing  two  parts  tin  and  one 
part  lead  has  the  lowest  melting  point  of  any  alloy  of  the 
two  metals.  It  is  called  the  eutectic  alloy.  The  freezing 
curve  of  a  series  of  lead-tin  alloys  is  given  in  Fig.  74. 

The    characteristics    of    a   chemical   compound  are   its 
absolute  constancy  of  composition  with  regard  to  both  the 
nature  and  proportions 
of  the  elements  it  con- 
tains, and  the  complete 
merging  of  the  proper- 


350 
Lead 
300 


^ 

S  250 


^oo 

I  '5° 
^  too 


10    20  30    4-0   50  60    70  80  90   100 
Per  Cent-Tin. 

FlG.  74. 


ties  of  these  elements 
into  those  of  the  com- 
pound. When  a  body 
of  any  kind  is  dissolved 
in  a  liquid,  the  solute, 
as  the  dissolved  body  is 

called,  is  uniformly  distributed  through  the  solvent,  and 
the  solution  becomes  perfectly  homogeneous ;  it  is  said  to 
be  a  body  of  uniform  concentration.  A  solution,  however, 
differs  from  a  chemical  compound  in  that  the  proportions 
of  the  solute  and  the  solvent  may  vary  between  wide  limits — 
that  is,  from  a  very  small  proportion  of  the  solute  up  to  the 
saturation  point.  But  the  saturation  proportion  depends 
very  largely  on  the  temperature  of  the  solution,  and  in 
most  cases  is  lowered  by  a  reduction  in  its  temperature. 
Liquids  tend  to  freeze  when  they  are  cooled,  and  the  general 
result  of  dissolving  a  solid  in  a  liquid  is  to  lower  its 
freezing  point ;  but  the  extent  of  this  lowering  depends 
upon  the  nature  of  the  liquid  and  the  nature  and  proportion 


290  IKON  AND   STEEL. 

of  the  dissolved  solid.     Take  the  simple  case  of  common 

salt  dissolved    in    water,    and    suppose   that   the   solution 

contains  one  part  of  salt  and  nine  parts  of  water.     If  such 

a   solution  is   surrounded   by  a   freezing   mixture,   and   a 

thermometer  is  put  into  it,  the  effects  of  cooling  may  be 

watched.    The  temperature  falls  below  the  freezing  point  of 

water  0°  C.,  and  the  solution  still  keeps  perfectly  liquid  until 

the  thermometer  reaches  —  8°C.,  when  solid  commences  to 

separate.     If  this  is  removed  and  examined  it  is  found  to  be 

pure   ice,   so  that  the    concentration    of   the    salt   in    the 

solution  is  increased.     This   causes   a  further  lowering  of 

the  freezing  point,   and  the  temperature  again  falls,  with 

separation  of  more  ice.     The  lowering  of  temperature  and 

separation  of  ice  goes  on  until  the  concentration  reaches 

23*5  per  cent,  of  salt  and  76*5  per  cent,  of  water,  and  the 

temperature  falls  to  —22°  C.      The  solution  then  solidifies 

completely.     If  on  the  other  hand  the  solution  contains 

more  than  23*5  per  cent,  of  salt,  then  no  solidification  takes 

place  until  — 12°  C.  is  reached,  when    salt  commences  to 

crystallise  out,  and  separation  of  salt  with  lowering  of  the 

freezing  point  goes  on  until  —22°  C.  is  again  reached,  when 

the  remaining  solution  contains  23'5  per  cent,  of  salt,  and 

solidifies  completely  as  before.     Thus  there  is  one  particular 

concentration  from  which  it  is  impossible  to  separate  either 

the  solute  or  the  solvent  by  merely  cooling  the  solution,  for 

if  it  is  cooled  sufficiently  it  solidifies  as  a  whole.     This  is 

the  well-known  eutectic  solution,  which  has  always,  for  the 

same  solute  and  solvent,  a  constant  composition ;  but  it  is 

not  a  chemical  compound.     Guthrie,  its  discoverer,  called 

it  a  cryohydrate ;  but  it  is  not  a  hydrate,   for  when  the 

solid  eutectic  is  examined  under  the  microscope  it  is  found 

to  consist  of  a  mixture  of  ice  crystals  and  salt  crystals. 

The  solute  and  the  solvent  appear  to  mutually  reject  each 

other   at   the   moment  of  solidification ;    and   this  is  the 

probable  constitution  of  all  eutectic  mixtures.     Now,  if  a 


HEAT  TREATMENT  OF  IRON    AND  STEEL. 


291 


solution  containing  an  excess  of  either  the  solvent  or  the 
solute  over  the  eutectic  proportions  is  cooled  until  it 
solidifies,  without  removing  the  excess  as  it  crystallises  out, 
the  solid  will  consist  of  crystals  of  the  excess  constituent 
imbedded  in  the  matrix  of  the  eutectic,  and  this  will  appear 
when  the  structure  is  examined.  The  freezing  curve  of  a 
salt  solution  is  shown  in  Fig.  75. 

Solid   Solutions. — Suppose   a    solution    to   become    solid 
without  any  separation  whatever  of  its  constituents  taking 
place,  it  would  then  retain  its  uniform  concentration  and 
homogeneousness,  and    be  in  every 
particular  the  same  as  a  liquid  solu- 
tion, but  in  the  solid  state.     Then 
suppose    that    a    lowering    of    the 
temperature   of    this   solid   solution 
caused  a  separation  of  one  or  other 
of  the  constituents,  this  separation 
would  go  on  until  the  eutectic  pro- 
portions   were    reached,   and    then 
further  cooling  would  not  effect  any       '"'0( 
further  separation  of  either  consti- 
tuent alone,  and  the  solid  mass  would 
have  the  same  general  structure  as 
a  solidified  solution  containing  an    excess 
stituent  over  the  eutectic  proportions. 


30 


* 


-22 

-30- 


Eutectic 


5     10    15  20   25  30 
Percent  Salt. 

FlG.   75. 


of  either  con- 
This  is  the  modern 
idea  of  a  solid  solution,  as  distinguished  from  a  solidified 
solution  which  need  not  be  homogeneous  when  just  solidi- 
fied, and  in  which  change  of  temperature  within  ordinary 
limits  does  not  cause  further  separation  of  the  constituents. 
Solution  of  Carbon  in  Iron. — Molten  iron  will  dissolve 
carbon  in  much  the  same  way  that  water  dissolves  salt, 
and  as  much  as  7  per  cent,  of  the  element  will  pass  into 
solution  under  proper  conditions.  The  melting  point  of 
pure  iron  is  about  1,600°  C.,  and  the  presence  of  carbon 
lowers  it  in  just  the  same  way  that  salt  lowers  the  freezing 

u  2 


292  IRON  AND   STEEL. 

point  of  water.  A  molten  mass  of  iron  containing  upwards 
of  5  per  cent,  of  carbon  deposits  graphitic  carbon  as  it  cools, 
so  that  when  the  temperature  falls  to  1,130°  C.  the  solution 
contains  4'3  per  cent,  of  carbon.  As  this  is  the  composition 
of  the  iron-carbon  alloy  of  lowest  melting  point  the  whole 
mass  becomes  solid.  The  eutectic  is  said  to  contain  2*3  per 
cent,  of  graphite,  and  the  other  constituent  is  the  solid 
solution  of  carbon  in  y-iron,  to  which  the  name  austenite 
has  been  given.  In  its  saturated  form  it  contains  about 
2  per  cent,  of  carbon.  When  the  molten  alloy  contains  less 
than  4'3  per  cent,  of  carbon  it  deposits  austenite  as  it  cools, 
instead  of  graphite.  The  eutectic  has  not  been  traced  in 
steels  containing  less  than  1*2  per  cent,  of  carbon,  so  that 
at  1,130°  C.  iron  can  hold  1*2  per  cent,  of  that  element  in 
solid  solution.  It  must  be  borne  in  mind  that  austenite  is 
similar  to  other  solutions  in  that  its  concentration  may 
vary.  Thus  its  carbon  ma}7  vary  from  0  to  2  per  cent.,  and 
this  will  cause  variation  in  its  properties.  The  cooling 
curve  is  shown  in  the  upper  range  (1600°  C.  to  1130°  C.) 
of  Fig.  77.  The  carbon  in  the  molten  alloy  is  regarded 
by  some  authorities  as  being  in  the  elemental  form, 
but  Professor  Sauveur  is  of  opinion  that  it  is  present 
as  carbide  of  iron.  Mr.  Stead  also  favours  this  view, 
and  brings  forward  the  effect  of  chill  casting  on  molten 
pig  iron  in  support  of  it.  It  is  said,  however,  that 
the  carbide  Fe3C  is  dissociated  above  1,050°  C.,  and  only 
forms  below  that  temperature.  Also,  that  at  1,000°  C., 
iron  can  hold  more  than  1*2  per  cent,  of  carbon  in  solid 
solution,  due  to  its  being  in  the  form  of  carbide.  But 
whichever  view  is  taken,  the  fact  remains  that  a  number 
of  important  changes  take  place  in  the  cooling  solid,  and 
much  experimental  work  has  been  done  in  investi- 
gating them.  It  is  almost  invidious  to  select  from  the 
many  distinguished  men  who  have  taken  up  this  work, 
but  the  names  of  the  late  Sir  W.  Roberts-Austen, 


HEAT  TREATMENT  OF  IEON  AND  STEEL.          293 

Osmond,  and  Le  Chatelier  must  always  occupy  a  foremost 
place. 

The  allotropic  modifications  of  iron  are  supposed  to  play 
an  important  part  in  the  constitution  of  steel.  Thus  /?-iron 
is  capable  of  forming  a  solid  solution  with  carbon,  but 
a-iron  does  not  dissolve  that  element.  Now  the  /3  to  a 
range  is  890°  C.  to  750°  C.  in  pure  iron,  but  the  presence  of 
carbon  retards  the  passage  from  the  /3  to  the  a  form. 
Speaking  generally,  there  is  always  a  certain  amount  of 
lag  during  the  passage  of  an  element  from  a  higher  to  a 
lower,  or  more  stable,  allotropic  form.  This  lag,  which  is 
caused  by  a  kind  of  sluggishness  or  disinclination  on  the 
part  of  the  element  to  alter  its  form,  is  accentuated  in  the 
case  of  iron  by  the  presence  of  carbon.  AVhen  pure  iron  is 
heated  up,  the  points  Ac2  and  Ac3  corresponding  to  Ar2  and 
Ar3  on  the  cooling  curve  occur  at  rather  higher  temperatures, 
and  the  lag  in  the  case  of  the  pure  element  thus  rendered 
evident. 

In  much  the  same  way  a  solution  may  become  super- 
saturated when  carefully  cooled  below  its  point  of  saturation, 
without  any  separation  of  solid.  Similarly  a  liquid  may 
be  supercooled,  that  is,  cooled  below  its  freezing  point, 
without  freezing.  A  body  in  this  supersaturated  or  super- 
cooled condition  is  in  unstable  equilibrium,  and  when 
solidification  does  take  place  there  is  a  rise  in  temperature 
due  to  the  evolution  of  heat  that  marks  the  passage  of  the 
liquid  to  the  solid  state.  Water,  for  example,  may  be 
cooled  several  degrees  below  its  freezing  point  without 
solidifying,  but  if  the  smallest  crystal  of  ice  is  dropped  into 
the  supercooled  liquid  solidification  at  once  sets  in,  and 
the  temperature  rises  rapidly  to  the  normal  freezing  point 
of  the  liquid.  Similarly  crystals  of  thiosulphate  of  soda 
may  be  melted  and  cooled  to  the  temperature  of  the  atmo- 
sphere without  solidification,  but  the  smallest  crystal  of  the 
salt  will  induce  crystallisation  together  with  a  rapid  rise  in 


294  IEON  AND  STEEL. 

temperature  and  considerable  evolution  of  heat.  Similar 
phenomena  no  doubt  play  an  important  part  in  the  cooling 
of  steel  and  cast  iron. 

The  Phase  Rule. — Any  body,  a  mass  of  iron  for  instance, 
may   be   regarded    as    an   independent    system   made   up 
of   matter   and  energy,  and  such  a  system  is  said  to  be 
in  stable  equilibrium  when  there  is  no  inherent  tendency 
to    change    as    long    as    the    outside    conditions    remain 
the  same.     Such  a  system  may   consist  of  one  or  more 
components.     These  components  may  be  either  elements 
or    compounds    which    are    not    decomposed    under    the 
existing   conditions.      These  components   may  pass  from 
solid  to  liquid  or  liquid  to  gas,  and  rice  versa  ;  they  may 
be  grouped    together   in   various   ways ;    they   may   even 
combine    together   to    form    definite    compounds    and   be 
decomposed    again.      Every   homogeneous   entity   in   the 
system,    whether  it  consists  of  one  or  more  of  the  com- 
ponents, is  called  a  phase,  wrhich  may  be  either  solid,  liquid, 
or  gaseous.     That  is,  a  phase  does  not  necessarily  indicate 
the  particular  physical  state  in  which  the  components  of 
the  system    exist.     It   may  be   anything   in  the  form  of 
matter   provided   it   is   homogeneous.      Thus   water   is   a 
system  of  one  component  which  may  exist  in  three  phases, 
solid,  liquid  and  gaseous.     On  the  other  hand,  a  solution 
of  salt  in  water  is  a  system  of  two  components  with  one 
phase,  that  is  a  homogeneous  liquid  solution.     A  system 
has  certain  properties  that  may  vary,  and  these  are  known 
as  the  variables  of  the  system.      Thus  in  a  simple  gas 
system  there  are  three  variables — volume,   pressure,  and 
temperature — and  two  of  these  must  be  known  before  the 
state  of  the  system  can  be  strictly  defined.     In  the  case  of 
a  solid  system  pressure  may  be  neglected,  which  simplifies 
the  matter  somewhat.     Thus  volume  or  concentration  and 
temperature  only  need  be  considered. 

Systems  are  said  to  have  one  or  more  degrees  of  freedom 


HEAT  TREATMENT  OF   IRON  AND  STEEL.          295 

when  they  can  survive  a  change  in  one  or  more  of  these 
variables  ;  but  no  degree  of  freedom  when  they  cannot 
survive  even  the  slightest  change  in  the  variables.  Thus 
there  is  only  one  temperature  and  pressure  at  which  the 
one  component  system  water  can  exist  in  the  three  phases, 
ice,  water,  and  vapour.  With  the  slightest  alteration  of 
either  temperature  or  pressure  one  of  these  phases  must 
eventually  disappear.  This  is  summed  up  generally  in  the 
Phase  Ilnle  formulated  by  Gibbs,  and  expressed  by  the 
equation  : 

p  =  c  +  2  -  P. 

F  denotes  the  number  of  degrees  of  freedom  ;  C  the 
number  of  components  ;  P  the  number  of  phases. 

Thus,  when  the  system  water  is  in  three  phases,  ice, 
water,  vapour,  the  equation  becomes  : 

F  =  l  +  2-3  =  0, 

or  there  are  no  degrees  of  freedom  ;  but  when  it  exists  in 
the  two  phases,  liquid  and  vapour,  then  : 


and  the  system  has  one  degree  of  freedom,  or  is  mono- 
variant. 

It  is  to  be  remembered  that  the  phase  rule  does  not  deal 
with  the  quantities  of  the  phases,  but  only  with  their 
existence.  There  may  be  much  or  little  of  a  particular 
phase. 

Now,  when  concentration  and  temperature  only  are 
considered,  the  equation  becomes  : 

F  =  C  +  1  -  P. 

Thus  the  molten  lead-tin  alloy  already  mentioned  is  a 
system  of  two  components  and  one  phase,  therefore  it  has 
two  degrees  of  freedom,  or  is  di-variant  ;  but  when  one  of 


296  IRON  AND   STEEL. 

the  metals  commences  to  freeze  out  there  are  two  phases, 
and  when  the  eutectic  begins  to  solidify  the  other  metal  is 
added  as  a  third  phase.  The  system  thus  becomes  mono- 
variant,  and  finally  in-variant.  The  eutectic  is  not  a  phase, 
for  it  is  not  homogeneous,  consisting  as  it  does  of  a  mixture 
of  the  two  constituents  of  the  system. 

Then  consider  the  case  of  molten  iron-carbon  alloy  ;  it  is 
a  di- variant  system  of  t\\ro  components,  iron  and  carbon, 
and  one  phase,  the  liquid  solution.  As  it  cools  either  the 
solid  solution  or  graphite  crystallises  out,  and  the  system 
becomes  mono-variant.  Then  when  the  eutectic  commences 
to  solidify  a  third  phase  is  added,  and  the  system  becomes 
in-variant.  One  or  other  of  these  phases  must  now 
disappear,  and  it  is  the  liquid  solution,  for  the  mass 
solidifies  ;  it  then  consists  of  two  phases,  graphite  and 
solid  solution,  when  the  carbon  exceeds  2  per  cent.,  and  of 
one  phase,  the  solid  solution,  when  less  than  2  per  cent,  of 
carbon  is  present. 

The  solid  continues  to  cool,  and  at  about  1,000°  C. 
cementite,  Fe3C,  forms  and  separates  from  the  solid 
solution.  There  are  now  three  phases,  ferrite,  cementite, 
and  graphite.  Now,  according  to  the  phase  rule,  the  system 
cannot  survive  a  further  change  in  temperature ;  one  or 
other  of  the  phases  must  disappear.  Prof.  Eoozeboom, 
who  gathered  together  the  results  of  Roberts-Austen  and 
others,  applied  the  phase  rule  to  their  elucidation,  and 
assumed  that  as  the  temperature  falls  below  1,000°  C. 
ferrite  and  graphite  unite  to  form  cementite  to  bring 
the  mass  again  into  stable  equilibrium.  But  there  seems 
to  be  conclusive  evidence  that  this  change  does  not  take 
place,  and  that  graphite,  once  formed  in  the  solid  mass, 
becomes  inactive.  Prof.  Sauveur  argues  that  this  is  no 
deviation  from  the  phase  rule,  but  that  the  graphite, 
once  separated,  no  longer  belongs  to  the  system.  He 
refers  to  the  Roberts-Austin-Roozeboom  diagram  as  being 


HEAT  TEEATMENT  OF  IRON  AND   STEEL. 


297 


classical,  and   it  is  without  doubt  a  very  fine  example  of 
generalisation.1 

Fig.  76  is  a  diagram  prepared  for  teaching  purposes,  in 
which  the  cooling  curves  of  a  series  of  carbon-steels 
obtained  by  Roberts- Austen  are  represented.  The  cooling 
curve  of  pure  iron  is  given  for  reference.  Temperatures 
are  plotted  on  the  vertical  line,  and  time  in  seconds  on  the 
horizontal  line.  The  first  arrest  point  Ar3,  which  indicates 
the  passage  of  y-iron  into  the  ft  form,  occurs  at  890°  C.  in 


30  40          50          60 

Time    in    Seconds. 

FIG.  76, 


pure  iron,  and  is  lowered  to  815°  C.  by  the  presence  of  O'l 
per  cent,  of  carbon.  The  second  arrest  Ar2,  which  takes 
place  at  750°  C.,  corresponds  to  the  passage  of  /3-iron  into 
the  a  form,  and  is  lowered  to  725°  C.  by  O'l  per  cent,  of 
carbon.  With  0'4  per  cent,  of  carbon  these  two  points  are 
brought  together  at  700°  C.  The  arrest  Ar1?  which  is 
observed  only  in  iron  containing  carbon,  occurs  at  640°  C. 
with  O'l  per  cent.,  and  at  650°  C.  with  0*4  per  cent,  carbon. 
With  1*3  per  cent,  of  carbon  the  three  points  coalesce  at 
680°  C. 

1  Journal  of  the  Iron  and  Steel  Institute,  No.  IV.,   1906. 


298  IRON   AND   STEEL. 

The  arrest  Ari,  which  is  only  observed  in  iron- carbon 
alloys,  is  due  either  to  the  formation  of  cementite  or  to  its 
separation  from  the  solid  solution,  the  latter  being  probably 
the  correct  explanation.  The  heat  developed  by  this 
separation  is  the  cause  of  recalescence,  and  is  augmented 
in  the  case  of  the  1*3  alloy  by  the  heat  due  to  other 
changes.  It  is  to  be  born  in  mind  that  these  changes  are 
not  by  any  means  instantaneous,  so  that  they  really  take 
place  within  definite  ranges  of  temperature,  but  for 
simplicity  these  are  represented  by  definite  temperatures. 

According  to  Sauveur,  steel  at  1,000°  C.  is  a  solid  solution 
of  carbide  in  y-iron,  known  as  austenite.  Within  the  first 
critical  range  it  is  transformed  into  the  solid  solution  of 
carbide  in  /3-iron,  marten  site.  Then  in  the  second  critical 
range  the  /?-iron  is  transformed  into  a-iron,  which  cannot 
form  a  solid  solution,  and  so  the  carbide  separates  and 
segregates  wTith  ferrite  to  form  pearlite.  The  resemblance 
of  this  change  to  the  solidification  of  a  eutectic  alloy  caused 
the  pearlite,  which  has  a  constant  composition  represented 
by  Fe3C  +  21  Fe,  to  be  regarded  as  a  eutectic,  but  objections 
were  raised,  and  Howe's  term  "eutectoid"  is  now  largely 
adopted.  The  composition  given  above  contains  0'89  per 
cent,  of  carbon,  and  the  terms  hypoeutectoid  and  hyper- 
eutectoid  have  been  applied  to  steels  containing  less  than 
and  more  than  0'9  per  cent,  of  carbon.  The  former  steels, 
when  in  the  soft  state,  consist  of  pearlite  and  ferrite,  and 
the  latter  of  pearlite  and  cementite.  Marten  site,  when  it 
has  the  same  composition  as  pearlite,  is  better  known  as 
hardenite. 

It  is  to  be  understood  that  the  shortening  of  the  range  in 
the  case  of  high  carbon  steels,  within  which  the  various 
changes  take  place,  does  not  mean  the  suppression  of  any 
one  of  them,  but  only  that  they  follow  one  another  in  the 
proper  order  within  the  contracted  range.  The  change 
from  austenite  to  martensite  can  be  partially  arrested  by 


HEAT  TREATMENT  OF  IEON  AND  STEEL. 


299 


1600- 


2%  Austemte- Graphite  Eutectic     \^/ forms 


Solid  Solution  Austenite 


Both  the  Excess  Graphite  and  the  Eutectic 
Graphite  pass  through  this  Range  unchanged 


The  Carbon  of  the  solid  Solution  (Austenite) 
combines  with  some  of  its  Iron  to  form  Fe3C 
(Cementite)  and  the  Excess  Cementite  is 
rejected  until  the  Carbon  Content  of  the 
remaining  Mass  is  reduced  to  0.80%(Hardemte) 


Hardenite  chanqes  here  into  Pearlite  Eutectoid 


SOD 


400 


2.00  3.00  400 

%  Carbon. 


Graphite 


From  Excess  Graphite 
rom  Eutectic  Graphite 


FIG.  77. — The  Roberts- Austen-Roozebooin  Curve  (Sauveur). 

quenching  the  steel  from  a  high  temperature  in  iced  brine. 
It  is  a  comparatively  soft  constituent  of  the  steel  in  which 
it  occurs,  as  it  can  be  scratched  with  a  needle.  The  change 
from  austenite  to  martensite  appears  to  be  fairly  rapid,  as 


300  IRON  AND   STEEL. 

a  steel  quenched  when  well  within  the  contracted  range  is 
almost  entirely  martensitic  in  character.  Some  of  the  tran- 
sition forms  between  martensite  and  pearlite  are  wrell  known, 
such  as  troostite  and  sorbite.  In  them  the  segregation 
of  the  pearlite  is  arrested  at  different  stages.  The  work  of 
Mr.  J.  E.  Stead  on  the  production  of  sorbite  in  large 
masses  of  steel  by  proper  heat  treatment  is  well  known, 
and  is  a  good  example  of  the  practical  application  of  the 
results  of  research  work.  Much  labour  has  been  bestowed 
upon  the  subjects  briefly  outlined  above,  and  there  is  little 
doubt  of  their  great  practical  value,  although  still  open  to 
controversy.  The  Eoberts-Austen-Koozeboom  curve,  as 
modified  by  Sauveur,  is  given  in  Fig.  77.  If  a  line  is 
drawn  through  the  diagram  parallel  to  the  temperature  line 
the  point  where  it  cuts  the  base  line  determines  the  per- 
centage of  carbon  in  the  alloy,  and  if  this  line  is  traced 
downwards  towards  the  base  line  the  changes  in  the  con- 
stitution of  the  alloy  as  it  passes  through  the  various 
temperature  ranges  are  indicated. 

HARDENING  AND  TEMPERING. 

When  a  piece  of  steel  containing  more  than  0*2  per  cent, 
of  carbon  is  raised  to  a  red  heat  and  then  suddenly  cooled, 
it  becomes  hard  and  brittle,  and  the  higher  the  percentage 
of  carbon  present  the  harder  and  more  brittle  does  the 
metal  become.  Further,  if  this  hardened  and  brittled 
metal  is  heated  to  a  temperature  between  200°  and  300°  C. 
the  hardness  is  somewhat  reduced,  and  the  brittleness  is 
very  largely  removed.  These  are  the  processes  of  hardening 
and  tempering. 

Quenching  Liquids. — The  hardness  of  a  given  sample  of 
steel  depends  upon  the  suddenness  with  which  it  is  cooled 
through  the  critical  range.  The  rate  of  cooling  depends 
upon  the  nature,  and  to  some  extent  upon  the  bulk  of  the 


HEAT  TREATMENT   OF  IEON  AND   STEEL.          301 

quenching  liquid.  The  difference  in  the  action  of  different 
liquids  is  well  shown  by  the  following  experiment :  Three 
similar  bars  of  the  same  steel  are  heated  together  to  the 
same  temperature,  separated,  and  plunged,  one  into 
mercury,  one  into  water,  and  one  into  oil.  When  they  are 
tested  for  hardness  the  bar  cooled  in  the  mercury  is  found 
to  be  the  hardest,  and  the  one  cooled  in  oil  the  softest,  the 
water  cooled  bar  taking  an  intermediate  place. 

Now  heat  escapes  from  a  body  in  three  ways,  (i)  radiation, 
by  which  the  heat  passes  from  the  body  through  space 
without  the  intervention  of  ordinary  matter  ;  (ii)  absorption 
into  the  gaseous,  liquid,  or  solid  matter  surrounding  the 
hot  body  ;  (iii)  conduction  through  the  surrounding  matter. 
All  these  are  more  or  less  concerned  in  removing  the  heat 
from  a  hot  body,  and  the  rate  at  which  it  is  removed 
depends  upon  the  properties  of  the  surrounding  bodies. 
Now  mercury,  though  not  such  a  good  absorber  of  heat  as 
water,  is  a  very  much  better  conductor,  and  this  property 
more  than  counterbalances  the  greater  absorbing  power  of 
the  water ;  hence  the  more  rapid  cooling  and  the  greater 
hardness  of  the  bar  quenched  in  it.  Also,  water  has  a 
greater  absorbing  power,  and  is  a  better  conductor  than  oil, 
which  explains  its  greater  hardening  property.  Mercury 
is  not  often  used  in  practice,  for  the  action  of  water  can  be 
increased  by  dissolving  a  body  such  as  common  salt  in  it, 
and  by  having  it  cold.  The  presence  of  the  salt  in  the 
water  increases  its  conductivity,  and  thus  causes  more 
rapid  cooling.  This  is  the  only  action  of  the  salt  and 
other  substances  added  to  the  water.  Ice  cold  water  is 
sometimes  used,  and  the  cause  of  its  increased  action  is 
obvious. 

There  is  for  each  quality  of  steel  a  temperature  limit 
above  which  the  metal  must  not  be  heated  in  the  hardening 
process,  so  that  if  extra  hardness  is  required  this  must  be 
arranged  for  in  the  quenching.  An  instructive  experiment 


302  IKON  AND   STEEL. 

in  this  connection  can  be  made  thus  :  a  bar  of  steel  12  inches 
long  is  nicked  at  every  inch,  and  heated  so  that  one  end  is 
at  a  white  heat,  and  the  other  at  a  very  low  red  heat,  the 
parts  in  between  being  at  intermediate  temperatures.  The 
whole  bar  is  then  quenched  in  cold  water,  and  broken  into 
pieces  across  the  nicks.  The  fractured  surface  of  the  piece 
that  was  hottest,  although  hard,  is  found  to  have  a  very 
open  crystalline  structure.  This  diminishes  in  the  other 
pieces  until  the  grain  becomes  close,  even,  and  velvety  in 
appearance,  and  this  piece  is  found  to  have  the  best  and 
most  uniform  hardness.  The  hardness  of  the  pieces  from 
the  other  end  is  defective,  and  the  grain  more  open.  It  is 
evident  from  this  that  there  is  a  temperature  range  within 
which  the  best  hardening  effects  are  obtained,  and  the 
metal  should  not  be  heated  above  it,  for  even  though  the 
steel  is  allowed  to  cool  to  the  proper  temperature  before 
quenching,  the  grain  does  not  close  again,  and  cracks  are 
likely  to  develop.  If  it  is  overheated  by  mistake  it  should 
be  allowed  to  cool  slowly,  and  then  be  heated  again  to  the 
proper  temperature  before  quenching.  This  will  modify, 
although  it  may  not  cure,  the  effects  of  overheating.  The 
temperature  should  be  high  enough  to  harden  the  metal 
sufficiently,  but  not  high  enough  to  open  the  grain.  A 
little  liberty  may  be  taken  with  the  lower  carbon-steels,  but 
absolutely  none  with  the  high  carbon  metal,  if  the  best  result 
is  to  be  obtained. 

A  tool  should  not  be  hardened  straight  from  the  forging 
process  even  though  it  be  hot  enough,  but  should  be 
allowed  to  cool  before  heating  for  hardening.  Tools  with 
sharp  edges  and  corners  should  be  allowed  to  cool  a  little 
before  quenching,  for  the  edges  are  usually  hotter  than  the 
main  mass  when  it  is  removed  from  the  heating  chamber. 
In  a  short  time  the  temperature  is  equalised,  and  the  body 
is  ready  to  be  plunged  into  the  cooling  liquid.  Large  tools 
are  more  difficult  to  harden  than  small  ones,  and  should  be 


HEA.T  TREATMENT  OF  IRON  AND   STEEL.          303 

raised  to  a  slightly  higher  temperature.  This  is  due  to  the 
more  rapid  quenching  of  the  smaller  body.  Also,  large 
tools  take  some  time  to  heat  up  to  the  necessary  temperature, 
so  that  oxidation  is  unavoidable  unless  their  surfaces  are 
protected.  This  may  be  done  by  coating  them  with  some 
substance  that  has  no  effect  on  the  steel.  Thus  common 
salt  and  borax,  or  borax  alone,  sprinkled  over  the  surface, 
melts  and  forms  a  glaze.  Soft  soap  rubbed  over  the  surface 
of  the  tool  protects  it  somewhat.  A  good  mixture  for  the 
purpose  consists  of  two  parts  of  charcoal  and  one  part  of 
yellow  prussiate  of  potash  boiled  with  water,  and  thickened 
with  gelatin.  When  the  tool  has  been  heated  to  a  dull  red 
it  is  dipped  in  and  out  of  this  mixture  until  it  is  well 
coated,  and  is  then  heated  up  for  hardening.  Scale  formed 
by  oxidation  is  a  bad  conductor,  and  when  firmly  adherent 
keeps  in  the  heat,  thus  rendering  the  cooling  slower,  and 
interfering  with  the  operation.  The  prevention  of  oxidation 
is  not  so  important  in  the  case  of  forged  tools  that  have  to 
be  ground  up  after  hardening ;  but  when  the  articles  are 
finished  before  they  are  hardened,  as  is  the  case  with  some 
machine  parts,  it  is  necessary  that  they  should  come  out 
bright,  or  at  any  rate  practically  free  from  scale.  Such 
articles  can  be  heated  by  immersing  them  in  a  bath  of 
molten  common  salt,  or  nitre,  the  temperature  of  which  is 
above  the  recalescence  point.  They  are  then  quenched  in 
the  usual  manner.  This  method  gives  uniform  results,  as 
the  temperature  of  the  bath  is  fairly  under  control.  The 
melting  point  of  common  salt  is  815°  C.,  and  that  of  nitre 
352°  C.  The  bath  is  usually  an  iron  pot  set  over  a  coal- 
fired  grate  by  which  it  is  heated.  Some  pots  are  gas-fired. 
Thin  films  of  oxide  may  be  removed  by  the  use  of  dilute 
hydrochloric  acid  (smoking  salts)  for  quenching.  This  is 
really  hardening  and  pickling  at  the  same  time,  but  it  must 
be  remembered  that  the  addition  of  the  acid  increases  the 
hardening  power  of  the  water.  A  solution  of  zinc  chloride 


304 


IKON  AND   STEEL. 


(killed  spirit)  is  also  used,  and  this  gives  a  pleasing  appear- 
ance to  the  surface  of  the  finished  work. 

When  the  heating  is  carried  on  in  a  smith's  fire,  or  in  a 
furnace  filled  with  flame,  the  surface  of  the  metal  is  exposed 
to  the  fuel  and  products  of  combustion,  and  the  metal  may 
be  injured  by  the  absorption  of  sulphur,  which  is  often 

present  in  the  fuel.  This 
method  may  be  described 
as  forge  hardening.  A 
safer  method,  now 
largely  used,  is  to  carry 
on  the  heating  in  a 
muffle  furnace,  the  heat- 
ing chamber  of  which  is 
completely  cut  off  from 
the  fuel  and  products  of 
combustion.  There  is 
more  liability  to  oxida- 
tion, but  as  the  surface 
of  the  metal  can  be  pro- 
tected, if  necessary,  this 
is  not  a  serious  objec- 
tion. Also,  two  or  more 
chambers,  one  above 
the  other  and  heated  to 

FIG.  78.-Muffle  Furnace.  ^'f'     temperatures, 

can    be   used,    and    the 

steel  heated  more  gradually  and  uniformly  by  passing  it 
from  chamber  to  chamber.  This  is  most  important,  for 
if  a  cold  tool  is  put  straightway  into  a  very  hot  space 
the  temperature  of  the  outside  is  suddenly  raised, 
causing  rapid  expansion  of  that  part  before  the  heat  is 
sufficiently  conducted  to  the  metal  beneath,  so  that  there 
is  a  greater  tendency  for  cracks  to  develop.  This 
improved  method  of  heating  is  rapidly  coming  into 


HEAT  TEEATMENT   OF  IKON  AND   STEEL. 


305 


use,  and  the  difficulties  of  the  hardener  are  gradually 
disappearing. 

With  tools  that  only  require  to  be  hard  in  one  part  the 
heating  must  be  conducted  so  that  the  temperature  grades 
off  uniformly,  for  if  there  is  a  sharp  break,  fracture  is  likely 
to  result.  Fig.  78  is  an  illustration  of  a  muffle  furnace 
with  two  heating  chambers. 

Tempering. — The  sudden  quenching  of  the  steel  prevents 
the  segregation  of  the  cementite,  and  thus  keeps  the  carbon 
in  solid  solution,  or  in  the  hardening  form.  As  the 
temperature  of  a  piece  of  hardened  steel  is  raised,  there  is 


Colour. 

Tempera- 
ture. 

Suitable  for 

Faint  yellow 
Straw      ,,              ... 

220°  C. 
230° 

Surgical  knives. 
Razors,  taps,  dies. 

Brown     ,,               ... 

255° 

Scissors,  shears. 

Purple  brown 

265° 

Axes,  planes. 

Purple          .... 

275° 

Table  knives,  punches,  chisels. 

Light  blue    .... 

288° 

Swords,  coiled  springs. 

Dark      ,,.... 

293° 

Fine  saws,  augurs. 

Nearly  black 

316° 

Hand  saws. 

a  tendency  towards  segregation  and  reduction  of  hardness. 
This  becomes  marked  at  about  200°  C.,  and  the  higher  the 
temperature  to  which  the  metal  is  raised  the  softer  does  it 
become.  If  a  piece  of  hardened  steel  is  rubbed  until  its 
surface  is  bright,  and  is  then  gradually  heated  in  contact 
with  air,  the  bright  surface  undergoes  change  due  to 
oxidation.  The  film  of  oxide  is  exceedingly  thin  at  first,  and 
colour  effects  are  observed  similar  to  those  on  a  soap  bubble. 
The  colour  of  the  film  furnishes  a  good  indication  of  the 
temperature  of  the  steel,  for  it  changes  as  the  metal  gets 
hotter.  When  the  proper  colour  appears  the  steel  is 
quenched.  The  above  table  gives  the  more  noticeable 
i.s.  x 


306  IEON  AND   STEEL. 

colours,  and  their  approximate  temperatures.  The  explana- 
tion of  the  internal  changes  in  the  light  of  the  solution 
theory  is  very  simple  :  the  cementite  in  the  solid  solution 
martensite  or  hardenite  commences  to  segregate,  and  thus 
softens  the  metal.  The  higher  the  temperature  the  greater 
the  segregation,  and  the  softer  the  temper  of  the  steel. 

The  simple  process  as  used  for  a  single  tool  may  he  thus 
described.  The  tool  is  rubbed  on  a  brick,  and  then  placed 
on  a  hot  bar  of  iron  with  the  brightened  surface  upwards. 
This  is  closely  watched  until  the  proper  colour  appears, 
when  the  tool  is  tipped  off  the  bar  into  the  quenching 
liquid. 

But  a  variety  of  methods  are  now  in  use  where  tempering 
is  carried  on  largely.  Lead  melts  at  326°  C.  and  alloys  of 
lead  and  tin  melting  at  lower  temperatures  are  easily 
obtained.  In  fact,  all  the  temperatures  given  above  can  be 
obtained  in  a  series  of  lead-tin  baths.  An  iron  vessel  con- 
taining the  alloy  and  heated  as  already  described  is  used. 
The  metal  or  alloy  is  kept  just  melted,  the  articles  are 
immersed  in  it,  and  when  they  have  reached  the  temperature 
of  the  bath,  are  removed  and  quenched.  Nor  is  it  necessary 
in  many  cases  to  make  the  tempering  a  separate  process, 
for  the  steel  at  the  hardening  temperature  may  be  plunged 
into  the  bath  and  held  there  till  it  comes  to  the  same 
temperature  ;  it  is  then  removed  and  plunged  into  water. 

Oil  baths,  which  are  readily  maintained  at  a  definite 
temperature,  are  largely  used  for  hardening  and  tempering. 
Of  course,  much  depends  upon  what  the  tool  or  part  is  to 
be  used  for.  In  some  cases  it  is  not  necessary  to  heat  up 
to  the  recalescence  point  before  quenching  in  the  oil  bath. 
An  oil  hardening  tank  75  feet  deep  and  containing  15,000 
gallons  of  oil,  is  in  use  at  Messrs.  Firth's,  Sheffield,  for 
hardening  heavy  gun  tubes.  It  is  served  by  a  50-ton  crane. 
Some  tools  are  made  in  large  quantities,  and  are  treated 
in  a  uniform  manner.  Files,  for  example,  are  covered  with 


HEAT  TREATMENT  OF  IRON  AND  STEEL.          307 

a  paste  of  salt  and  flour,  heated  in  a  coke  fire,  straightened 
on  a  block  with  a  lead  hammer,  and  then  dipped  into  a 
brine  bath.  Saws  are  quenched  in  whale  oil,  and  the  oil 
that  adheres  to  the  surface  burnt  off  to  temper  them. 
Large  pieces,  such  as  steel-faced  anvils,  are  sprayed  from 
above  with  water.  Very  thin  sheets  may  be  hardened  by 
quenching  them  between  thick  metal  plates,  which  treatment 
also  prevents  them  from  warping. 

Annealing. — The  hardening  effect  of  working  on  iron  and 
steel,  especially  on  the  cold  metal,  is  well  known,  and  is 
largely  due  to  the  internal  strains  set  up  in  the  metal  by 
the  external  stresses  brought  to  bear  upon  it.  The  operations 
having  the  greatest  effect  are  forging,  rolling,  and  wire 
drawing.  The  object  of  annealing  is  to  remove  these 
internal  strains,  or  to  redistribute  them.  Steel  hardened 
by  cold  or  nearly  cold  working  is  not  hard  in  the  same  sense 
that  quenched  steel  is  hard  ;  but  when  worked  hot  the 
hardness  may  be  due,  in  part  at  least,  to  the  arrest  of 
some  of  the  changes  that  take  place  on  slow  cooling.  The 
annealing  should  be  conducted  so  that  the  metal,  whether 
hard  from  working  or  from  quenching,  is  obtained  in  the 
softest  and  most  ductile  condition  possible,  and  the  resis- 
tance to  sudden  shocks  is  a  maximum.  Also  the  elastic  limit 
should  be  high.  It  may  be  stated  generally  that  the  higher 
the  percentage  of  carbon  in  the  metal  the  greater  the  care 
required  in  regulating  the  temperature  of  annealing.  The 
operation  should  be  conducted  as  far  as  possible  out  of 
contact  with  air,  to  prevent  oxidation,  particularly  so  with 
high  grade  steels,  as  some  of  the  carbon  itself  is  burnt  out. 

According  to  Brinnel,  steel  annealed  at  gradually  in- 
creasing temperatures  up  to  about  680°  C.  undergoes  very 
little  change  in  structure  as  far  as  the  grain  is  concerned, 
but  at  730°  C.,  just  above  the  recalescence  point,  the 
structure  becomes  fine  grained.  He  distinguishes  this 
important  range  of  temperature  by  marking  the  lower  limit 

x2 


308  IEON  AND  STEEL. 

by  the  letter  F  and  the  upper  limit  by  the  letter  TF.  These 
are  practically  the  same  as  the  arrest  points  Ari  and  Aci 
already  described.  Above  this  temperature  range  the  grain 
gets  coarser,  until  at  1,100°  C.  it  is  quite  coarse,  and  at 
1,400°  C.  it  is  very  coarse  grained  and  "burnt."  This 
burning  is  distinguished  from  simple  overheating  by  the 
extreme  brittleness  of  the  metal  both  hot  and  cold,  and  its 
coarse,  shining  fracture.  The  grains  are  probably  only 
slightly  coherent,  and  at  this  high  temperature  small 
quantities  of  occluded  gas  are  liberated,  the  pressure  of 
which  forces  the  grains  apart,  and  makes  the  structure  more 
open.  Air  can  thus  filter  in  and  the  grains  are  oxidised 
superficially.  The  oxygen  thus  introduced  may  also  assist 
in  opening  the  structure  by  forming  carbon  monoxide  with 
some  of  the  carbon,  which  by  its  pressure  would  help  to 
separate  the  grains.  If  this  is  true  it  becomes  clear  why 
high  grade  steel  is  more  easily  burnt  than  low  carbon  metal. 

Annealing  the  burnt  metal  at  a  lower  temperature  will 
not  cure  it,  as  it  cannot  close  up  the  grains.  Nor  is  such 
metal  benefited  very  much  by  hammering  or  rolling.  It 
must  be  melted  again,  so  that  it  is  best  for  burnt  metal  to 
be  scrapped  straightway.  On  the  other  hand,  metal  that 
has  been  simply  overheated  can  be  in  a  great  measure 
restored  by  annealing  at  a  lower  temperature,  and  by 
mechanical  working. 

According  to  Stead,  the  prolonged  heating  of  low  carbon 
steels  between  600°  C.  and  750°  C.  renders  them  coarsely 
crystalline,  but  not  necessarily  brittle.  On  reheating  to 
about  900°  C.  the  coarse  grain  and  brittleness  disappear. 
Thus  he  found  that  steel  rails  and  blooms  which  had  been 
rendered  dangerously  brittle  by  overheating  were  restored 
to  the  best  possible  condition  by  reheating  them  to  870°  C., 
and  without  working  them  down  to  a  smaller  size.  Test 
pieces  were  taken  from  these  bars  and  subjected  to 
alternating  stress  tests,  and  to  impact  tests. 


HEAT  TREATMENT  OF  IRON   AND   STEEL.          309 

Campion,  who  has  investigated  the  effects  of  heat  on 
steels  containing  from  O'l  to  0'5  per  cent,  of  carbon,  states 
that  the  best  temperature  for  annealing,  so  as  to  obtain  a 
high  elastic  limit  and  great  ductility,  lies  between  750°  C.  and 
850°  C.  The  metal  is  then  in  the  best  possible  condition 
to  resist  sudden  shocks.  The  higher  the  temperature  the 
shorter  the  time  the  metal  requires  to  be  exposed  to  it ; 
but  although  slower  heating  at  a  lower  temperature  may 
be  suitable  for  some  steels,  the  recalescence  point  must  be 
exceeded  to  obtain  the  finest  grain. 

Professor  Howe  also  emphasises  the  importance  of  a 
careful  regulation  of  the  temperature  during  annealing, 
which,  by  the  way,  he  calls  "  heat  refining,"  and  states 
that  it  must  be  carried  above  the  recalescence  point,  or  to 
the  W  of  Brinnel,  if  the  finest  grain  is  to  be  obtained. 
"Hammer  refining"  is  also  another  expressive  term  used 
by  Howe  in  dealing  with  the  effects  of  mechanical  work 
upon  the  hot  metal.  It  may  be  noted  here  that  the  effect 
of  work  of  any  kind  at  temperatures  below  a  dull  red  heat 
is  to  distort  the  grains,  but  this  distortion  and  its  effects 
can  be  removed  by  heating  the  metal  through  the 
range  V — W. 

The  usual  practice  with  heavy  gun  tubes,  large  axles,  etc., 
is  to  heat  to  about  800°  C.  and  quench  in  oil  at  20°  C. 
Then  reheat  to  550°  C.  This  considerably  increases  the 
resistance  of  the  metal  to  shock. 

From  what  has  been  said,  the  great  importance  of  the 
proper  heat  treatment  will  be  readily  understood,  if  the 
best  is  to  be  got  out  of  the  metal. 

The  term  annealing  is  also  used  in  connection  with  the 
heat  treatment  of  some  forms  of  cast  iron.  Grey  iron  when 
cast  into  large  pieces  is  sufficiently  soft  to  be  machined,  but 
there  is  often  a  thin  skin  of  hard  metal  to  be  removed  first. 
With  small  articles,  which  cool  rapidly  in  the  moulds,  the 
chilling  effect  is  much  more  marked,  and  the  skin  of  white 


310  IRON  AND  STEEL. 

metal  is  moderately  thick.  This  may  be  modified  by  pro- 
longed heating  in  a  slow  fire,  and  the  surface  can  then 
be  dressed.  Common  cutlery  is  often  produced  in  this 
way.  When,  however,  white  or  mottled  irons,  which  are 
low  in  silicon,  are  used,  the  nature  of  the  castings  is  the 
same  as  that  of  the  metal  from  which  they  are  cast.  The 
castings  are,  therefore,  hard,  brittle,  and  unworkable,  and 
must  be  annealed.  But  the  annealing  has  for  its  object 
the  decomposition  of  the  cementite,  and  the  liberation  of 
the  carbon  in  the  form  of  what  Ledebur  calls  "  temper 
carbon."  This  is  free  carbon  but  not  graphite,  and  it  gives 
to  the  fractured  surface  of  the  iron  a  black  velvety 
appearance,  which  has  gained  the  name  of  "  black  heart " 
for  the  castings  in  which  it  is  present.  To  bring  about 
this  change  the  castings  are  imbedded  in  sand  in  an  iron 
pot,  and  the  lid  luted  round  with  clay  to  exclude  the  air. 
The  pot  is  then  heated  in  a  furnace  to  a  temperature  of 
850°  C.,  and  maintained  at  this  heat  for  about  two  days. 
It  is  then  allowed  to  cool  down  slowly.  A  skin  of  malleable 
iron  is  formed  due  to  the  oxidising  effect  of  the  small 
quantity  of  air  in  the  box,  but  inside  this  is  the  black 
heart  peculiar  to  castings  of  this  class.  They  are  stronger 
than  similar  castings  made  from  grey  iron,  and  machine 
readily. 

For  "  malleable  castings  "  so  called,  the  process  is  some- 
what different.  They  are  cast  from  white  or  mottled  iron, 
and  are  glass  hard  and  brittle.  To  soften  them  and  render 
them  workable  they  are  imbedded  in  coarsely  powdered 
haematite  ore,  and  heated  in  cast  iron  pots  to  850°  C.  Two 
or  three  days  are  required  to  get  up  the  temperature,  and 
about  the  same  time  to  complete  the  annealing.  The  length 
of  time,  however,  depends  upon  the  size  of  the  pieces,  and 
the  extent  of  the  annealing  required.  The  operation  is 
sometimes  called  oxidising  cementation,  and  it  is  certain 
that  oxidation  takes  place  which  results  'in  the  removal  of 


HEAT  TREATMENT  OF   IRON  AND   STEEL.          311 

some  of  the  carbon  ;  but  the  principal  change  appears  to  be 
the  decomposition  of  cementite  and  the  liberation  of  its 
carbon,  either  as  finely  divided  graphite,  or  as  temper 
carbon.  Thus  a  malleable  casting  after  annealing  consists 
of  a  shell  of  iron  softened  by  the  removal  of  most  of  its 
carbon,  and  a  core  softened  by  the  liberation  of  its 
combined  carbon  as  graphite. 

MEASUREMENT  OF  TEMPERATURE. 

Specific  heat  and  temperature  are  regarded  as  the  two 
factors  of  heat  energy,  and  are  measured  by  reference  to 
arbitrary  standards.  Specific  heat  is  in  effect  the  capacity 
of  unit  weight  of  a  body  for  absorbing  heat,  while  tempera- 
tare  indicates  the  tendency  of  heat  to  escape  from  the  body. 
Generally,  when  heat  enters  a  body  its  temperature  rises, 
but  the  greater  the  specific  heat  of  the  body  the  smaller 
will  be  the  rise  in  temperature  for  a  given  quantity  of  heat 
absorbed.  "Whatever  may  be  the  capacity  for  heat  or  the 
size  of  the  body,  it  can  be  raised  to  a  given  temperature  if 
sufficient  heat  is  passed  into  it.  Thus  a  50  ton  ingot  may 
be  raised  to  the  same  temperature  as  one  weighing  a  pound, 
and  the  temperature  determined  from  either  of  them,  for 
it  is  the  same  in  both.  Temperature  bears  much  the  same 
relation  to  heat  that  height  of  level  does  to  water.  The 
pressure  of  the  water  in  a  tank  depends  upon  the  height  of 
the  level  and  not  upon  the  dimensions  of  the  tank.  The 
fixed  points  for  the  arbitrary  measurement  of  temperature 
are  the  freezing  and  boiling  points  of  water.  On  the 
Centigrade  scale  the  interval  between  these  two  points  is 
divided  into  100  parts  or  degrees.  Thus  0°  C.  is  the  freezing 
point,  and  100°  C.  the  boiling  point,  of  water.  1,000°  C. 
is  equal  to  ten  times  this  interval  of  temperature.  On  the 
Fahrenheit  scale  the  interval  is  divided  into  180  parts  and 
32  are  added  below  the  freezing  point,  so  that  the  freezing 


312  IRON  AND   STEEL. 

point  is  32°  F.  and  the  boiling  point  212°  F.  Degrees  on 
one  scale  can  be  expressed  in  degrees  on  the  other  by  the 
following  simple  formulae  :— 

C°  =  5  (F°  -  32)  ;   F°=  |  C°  +  32. 
9  5 

The  instruments  for  measuring  temperatures  up  to  300°  C. 
are  usually  called  thermometers,  and  are  mostly  based  upon 
the  expansion  of  a  liquid  as  its  temperature  rises.  Mercury 
is  the  common  liquid  for  the  purpose,  and  a  few  minutes 
spent  with  a  mercurial  thermometer  will  render  its  action 
perfectly  clear.  For  measuring  higher  temperatures  the 
instruments  depend  upon  other  principles,  and  are  known 
as  pyrometers.  A  large  number  of  such  instruments  have 
been  devised  for  the  purpose.  The  two  forms  most  generally 
used  are  electrical  in  principle. 

The  Resistance  Pyrometer. — The  Siemens  pyrometer 
depends  upon  the  increase  in  the  resistance  of  a  thin 
platinum  wire  to  the  passage  of  an  electric  current  through 
it  as  the  temperature  to  which  it  is  exposed  rises,  and  the 
measure  of  this  increase  in  resistance  is  also  a  measure  of 
the  increase  in  temperature.  By  correlating  these  the 
temperature  is  determined.  A  modern  portable  form  of 
this  instrument,  made  by  the  Cambridge  Scientific  Instru- 
ment Company,  is  shown  in  Fig.  79.  The  porcelain  or 
steel  tube  contains  a  coil  of  thin  platinum  wire  wound  on 
a  mica  frame.  The  free  ends  of  the  coil  are  connected  by 
stout  leads  to  the  indicator.  The  tube  is  inserted  in  the 
hot  space  the  temperature  of  which  is  to  be  determined, 
when  the  resistance  of  the  coil  increases  until  the  space  and 
the  tube  are  at  the  same  temperature.  This  resistance  is 
then  balanced  by  an  opposing  resistance  in  the  recorder 
that  is  put  into  the  circuit  by  turning  a  milled  head  con- 
nected with  it.  The  balance  is  indicated  by  a  magnet 
needle  which  points  to  zero  on  the  scale  when  the  balance 


HEAT  TREATMENT  OF   IRON   AND  STEEL.          313 

is  made.     The   temperature  is  then  read  off  on  the  tem- 
perature scale.      These   instruments  are    calibrated    with 


PIG.  79. — Resistance  Pyrometer. 

great  care,  and  give  good  results.  In  Fig.  14  a  labourer  is 
shown  taking  the  temperature  of  the  hot  blast  with  one  of 
these  instruments. 

The  Thermo-Electric  Pyrometer. — This  instrument  depends 
upon  the  fact  that  if  two  wires  of  different  metals  or  alloys 


314  IRON  AND   STEEL. 

are  twisted,  soldered,  or  welded  together  at  both  ends  so  as 
to  form  a  closed  loop,  and  if  one  of  the  se  junctions  is  heated 
while  the  other  is  kept  cool  an  electric  current  will  circulate 
in  the  wire.  This  current,  although  very  small,  can  be 
made  to  deflect  a  sensitive  galvanometer  needle,  and  a 
record  of  its  strength  is  thus  obtained.  As  the  deflection 
of  the  needle  is  proportional  to  the  strength  of  the  current, 
and  the  strength  of  the  current  is  proportional  to  the 
temperature  of  the  junction,  this  last  quantity  can  be 
determined.  Various  metals  and  alloys  might  be  used  for 
the  junction,  but  for  recording  high  temperatures  the 
platinum  and  platinum-rhodium  alloy  introduced  by  M.  Le 
Chatelier  is  the  best.  In  the  Roberts-Austen  form  of  this 
pyrometer  the  galvanometer  carries  a  small  mirror 
which  is  made  to  reflect  a  small  spot  of  light  on  to  a 
photographic  plate.  When  the  galvanometer  is  deflected 
by  a  current  passing  through  it  the  mirror  is  deflected  also, 
and  the  spot  of  light  travels  along  the  plate  in  a  horizontal 
direction.  If  at  the  same  time  the  plate  is  caused  to 
move  at  a  uniform  rate  the  spot  of  light  will  trace  a 
curve  upon  it  that  will  come  into  view  when  the  plate  is 
developed,  and  will  thus  form  a  permanent  record  of  the 
variation  in  temperature  of  the  thermo  junction.  Apparatus 
based  upon  these  principles  was  used  for  obtaining  the  data 
from  which  the  curves  given  in  Fig.  77  were  plotted. 

A  portable  pyrometer  of  this  type  is  made  for  use  in 
works.  It  consists  of  a  platinum  and  platinum-rhodium 
junction  inserted  in  a  porcelain  or  steel  tube  and  a  recorder. 
The  wires  are  carefully  insulated  from  each  other,  and  the 
cold  junction  is  contained  in  a  box  at  the  top  of  the  tube, 
together  with  two  other  junctions — copper-platinum  and 
copper  platinum-rhodium—formed  by  putting  the  copper 
leads  from  the  galvanometer  into  the  circuit.  But  as  these 
junctions  are  all  in  the  same  space  they  are  kept  at  the 
same  temperature,  which  is  registered  by  a  thermometer 


HEAT  TEEATMENT   OF   IRON  AND   STEEL.          315 

and  is  thus  known.  The  galvanometer  is  not  always  of  the 
reflecting  type,  but  in  some  forms  an  automatic  record  can 
be  obtained  from  a  curve  traced  on  the  prepared  surface  of 
a  revolving  drum,  which  may  be  arranged  to  revolve  once 
in  a  given  number  of  hours,  say  up  to  twenty-four  hours. 
The  recording  part  of  the  apparatus  may  be  placed  at  any 
convenient  distance  from  the  junction,  and  connected  with 
it  by  leads.  The  manager's  office  is  a  good  place  for  it. 

In  the  portable  type,  for  taking  the  temperature  at 
intervals,  it  is  read  on  a  dial  plate  attached  to  the  recorder 
box.  Each  instrument  has  to  be  calibrated  before  it  is 
used,  and  this  is  done  by  means  of  substances,  principally 
metals,  of  which  the  melting  points  are  accurately  known. 
To  do  this  all  the  junctions  are  brought  to  the  same 
temperature,  and  the  zero  point,  where  the  pointer  comes 
to  rest  on  the  galvanometer  scale,  is  marked.  A  piece  of 
one  of  the  metals  is  melted  in  a  small  crucible  imbedded 
in  a  mass  of  sand  contained  in  a  larger  crucible.  The 
whole  is  then  removed  from  the  furnace  and  the  thermo 
junction,  incased  in  a  thin  clay  tube,  held  in  the  molten 
metal.  When  the  freezing  point  of  the  metal  is  reached 
the  cooling  is  arrested  for  a  time,  and  the  position  of  the 
pointer  on  the  galvanometer  scale  remains  practically 
stationary  until  the  metal  is  solid.  This  point  is  noted, 
and  other  metals  are  treated  in  the  same  manner.  In  this 
way  a  number  of  points  are  obtained  on  the  scale,  which  is 
then  divided  in  proportion.  The  strictly  correct  method  is 
to  plot  a  curve  from  the  data  thus  obtained,  and  so  find  the 
intermediate  points.  It  is  said  that  these  instruments, 
when  correctly  calibrated,  will  read  up  to  1,600°  C. ;  but  the 
shorter  the  range  the  more  open  it  is.  The  actual  tempera- 
ture registered  is  the  difference  between  the  temperatures 
of  the  hot  and  cold  junctions  plus  the  temperature  of  the 
cold  junction.  The  temperature  of  the  recalescence  point 
of  steel  is  easily  determined  by  one  of  these  instruments. 


316 


IRON  AND   STEEL. 


The  steel  bar,  which  has  a  hole  drilled  in  it  to  take  the 
thermo-junction,  is  heated  to  a  bright  red  heat,  the  junction 
inserted,  and  the  whole  allowed  to  cool.  The  pointer  is 
deflected  and  then  travels  back  across  the  scale  towards 
the  zero  point,  but  when  the  recalescence  commences  it  is 


FIG.  SO. — Radiationi  Pyrometer. 

again  deflected,  thus  showing  a  sudden  increase  in  the  tem- 
perature of  the  cooling  steel.  When  the  recalescence  is 
passed  the  pointer  resumes  its  journey  towards  zero. 

The  Fery  Radiation  Pyrometer. — The  drawback  to  the 
resistance  and  thermo-electric  p3a*ometers  is  that  there  is  a 
limit  to  the  temperature  to  which  they  can  be  exposed,  as 


HEAT   TEEATMENT   OF    IRON  AND   STEEL.         317 

the  themometric  portions  of   these   instruments   must  be 
actually  in  the  hot  space  the  temperature  of  which  is  to  be 
measured.      This  is  obviated  in  the  Fery  instrument  by 
having  the  thermo-couple  outside  the  space,  and  focussing 
the  radiations  from  the  furnace  or  other  hot  body  upon  it. 
The  pyrometer  consists  of  a  small  reflecting  telescope,  the 
concave  mirror  of  which  receives  the  radiations  from  the 
hot  body,  and  brings  them  to  a  focus  on  a  copper-constantan 
thermo- junction  placed  there  to  receive  them.      The  free 
ends  of  the  junction  are  connected  with  binding  screws  on 
the  side  of  the  telescope  tube,  and  leads  pass  from  these  to 
the    sensitive     galvanometer    that    registers    the   current 
generated.     It  is  evident  that  the  hotter  the  body  is  from 
which  the  radiations  come  the  higher  will  be  the  tempera- 
ture of  the  junction,  and  the  stronger  the  current  registered 
by  the  galvanometer.      Theoretically,  the  distance  of  the 
instrument  from  the  hot  body  would  have  to  be  taken  into 
account,  as  some  radiation  is  absorbed  by  the  air  through 
which    it    passes,    but    practically    it    makes    very    little 
difference  whether  the  space  between  is  5  feet  or  50  feet. 
A  hole  leading  into  a  furnace  is  required  for  sighting,  but 
a  red  hot  ingot  or  a  stream  of  molten  steel  may  be  sighted 
direct.      On  looking  through  the  eye  piece  of  the  telescope 
the  junction  is  seen  as  a  black  disc  in  the  middle  of  the 
field,  and  the  image  of  the  hot  body  shows  as  two  half- 
circles   formed  by  two   mirrors   placed  near  the  junction. 
The   pyrometer  is  in  the  proper  position  for  taking  the 
temperature   when    these   two    half-circles    join    to    form 
a  complete  circle  that  clearly  over-laps  the  junction  disc. 
The  galvanometer  is  calibrated  to  read  degrees  Centigrade. 
Two   temperature   scales,  one  from   600°  C.   to  1,300°  C. 
and  another  from  1,000°  C.   to    2,000°  C.,  are    ordinarily 
divided  on  the  galvanometer.     When  high  temperatures 
are  to  be  registered  a  diaphragm  is  used  to  cut  off  a  portion 
of  the  heat  from  the  telescope.     The  temperature  of  the 


318  IRON  AND   STEEL. 

hot  junction  rarely  exceeds  80°  C.,  so  that  it  is  under  perfect 
control,  and  the  sighting  is  an  easy  matter.  A  permanent 
record  for  a  given  period  can  be  obtained  by  using  a  thread 
recorder  in  place  of  the  direct  reading  galvanometer. 

Professor  Fery  has,  by  using  one  of  these  instruments, 
estimated  the  temperature  of  the  sun  to  be  7,800°  C.,  and  it 
is  certain  that  they  give  the  very  best  means  at  present 
available  of  determining  the  temperature  of  electric 
furnaces  and  other  very  hot  bodies.  Fig.  80  shows  the 
general  form  of  the  pyrometer  as  used  in  works. 


CHAPTEE  XIII. 

ELECTRIC     SMELTING. 

THE  employment  of  the  energy  of  an  electric  current  for 
doing  various  kinds  of  work  is  now  well  known.  Heating, 
lighting,  and  traction  are  the  most  familiar,  but  the 
chemical  action  of  the  current  is  also  largely  used  in 
manufacturing  processes.  There  are  a  variety  of  ways  in 
which  an  electric  current  with  its  accompanying  energy 
can  be  generated,  but  in  whatever  manner  it  is  brought 
into  existence  an  equivalent  quantity  of  some  other  form  of 
energy  disappears.  The  only  way  of  generating  electricity 
on  the  large  scale  for  practical  use  is  by  means  of  the 
dynamo,  and  this  machine  requires  to  be  driven  by  power 
of  some  kind.  The  common  sources  of  such  power  are 
steam,  water,  and  combustible  gas,  and  which  of  these 
sources  is  the  most  economical  depends  upon  surrounding 
conditions. 

There  are  two  principal  types  of  current  generators  : 
direct-current  dynamos  and  alternators.  In  machines  of 
the  first  type  the  effective  parts  are  so  arranged  that  a 
continuous  current  flows  through  an  outside  conductor 
connecting  the  terminals  or  brushes  which  press  upon  the 
revolving  commutator.  That  is,  the  main  current  is 
always  in  the  same  direction,  for  one  terminal  is  constantly 
at  a  higher  potential  than  the  other,  and  it  is  assumed  that 
electricity  flows  from  points  of  higher  potential  to  points  of 
lower  potential  through  a  conductor  joining  them.  In 
machines  of  the  second  type  the  arrangement  is  such  that 
the  current  ebbs  and  flows  with  a  concertina-like  motion  in 


320  IEON  AND   STEEL. 

the  conductor  joining  the  terminals,  so  that,  in  effect,  the 
main  current  is  made  up  of  series  of  currents  in  opposite 
directions.  This  is  the  result  of  the  constantly  changing 
potential  of  the  terminals,  for  when  one  is  high  the  other 
is  low,  and  they  change  alternately,  so  that  currents  passing 
between  them  alternate  in  direction. 

The  action  of  these  current  generators  depends  upon  the 
rapid  cutting  of  the  lines  of  force  in  a  powerful  magnetic 
field  by  properly  arranged  coils  of  insulated  copper  wire, 
The  larger  the  number  of  lines  cut  in  a  given  time  the 
higher  is  the  potential  at  which  the  current  is  generated. 
Therefore,  for  a  given  coil  the  more  powerful  the  field,  and 
the  faster  the  coil  cuts  through  it,  the  higher  is  the  average 
potential  generated  in  the  coil.  But  as  the  coil  moves  into 
the  field  the  potential  rises  to  a  maximum,  and  as  it  moves 
out  of  the  field  the  potential  falls  to  a  minimum,  so  that 
there  is  a  constant  rise  and  fall  with  its  accompanying 
alternation  in  the  direction  of  the  current,  for  the  current 
ebbs  and  flows  in  the  coil  in  exactly  the  same  way  that  it 
does  in  the  conductor  joining  the  terminals.  This  is  the 
natural  order  inside  the  machine,  so  that  in  its  simplest 
form  it  is  an  alternator. 

The  coils  are  fixed  to  a  spindle  working  in  bearings,  and 
having  a  driving  pulley  at  one  end.  The  other  end  is  fitted 
with  two  copper  rings  insulated  from  each  other,  to  which 
the  two  free  ends  of  the  coils  are  joined.  The  whole  is 
called  the  armature.  The  electro-magnets,  which  consist  of 
soft  iron  parts  surrounded  by  insulated  coils  of  copper  wire, 
form  part  of  the  fixed  portion  of  the  machine.  Two  contact 
pieces  press  against  the  rings,  and  are  connected  with  the 
terminals  from  which  the  power  is  drawn  off  for  use.  In 
direct  current  machines  the  end  of  the  armature  is  divided 
into  a  large  number  of  copper  segments  insulated  from  each 
other,  and  to  these  the  ends  of  the  coils  are  so  connected 
that  when  the  two  contact  pieces,  or  brushes,  are  pressed 


ELECTRIC  SMELTING. 


321 


against  opposite  ends  of  a  diameter,  the  current  is  always 
passing  out  of  the  end  of  the  coil  connected  with  the 
segment  being  pressed  upon  by  the  one  brush,  and  passing 
into  the  coil  connected  with  the  segment  being  pressed 
upon  by  the  other  brush.  The  terminal  of  the  machine 
connected  with  the  high  potential  brush  is  said  to  be  the 
positive  4-  terminal,  and  that  with  the  low  potential  brush 
the  negative  —  terminal.  This  divided  end  is  called  the 
commutator,  and  the  greater  the  number  of  segments  in  it 
the  nearer  the  cur- 
rent approaches  to  a 
continuous  one 
through  the  outside 
conductor.  Thus  in 
alternators  the  cur- 
rents are  allowed  to 
flow  as  they  are  gene- 
rated, and  in  direct- 
current  machines 
they  are  diverted  into 
one  direction.  The 
electro-magnet  in 
either  machine  is 
excited  by  a  direct 
current  which,  in  the  case  of  the  alternator,  is  furnished 
by  a  small  direct-current  dynamo  attached  to  the  frame, 
and  in  the  case  of  the  direct-current  machine  from  the 
armature  of  the  machine  itself. 

Alternators  are  either  monophase  or  polyphase,  according 
to  the  number  and  arrangement  of  their  coils.  In  polyphase 
machines  a  pair  of  rings  and  leads  may  be  used  for  each 
phase,  or  they  may  be  combined  with  a  common  return. 
In  a  well  designed  machine  a  very  large  proportion  of  the 
mechanical  power  used  in  driving  it  is  converted  into 
electrical  energy  to  pass  out  of  the  terminals  with  the 

i.s.  Y 


FIG.  81. — Alternators  in  Position. 


322  IRON  AND   STEEL. 

current.  Alternators  are  by  far  the  best  for  heavy  work  for 
which  the  alternation  in  the  direction  of  the  current  is  of 
no  importance.  A  difference  of  potential  up  to  16,000  units 
may  be  generated  in  them  with  safety,  but  in  direct-current 
machines  the  limit  of  safety  is  about  2,000  units.  Very 
large  and  powerful  alternators  are  now  being  designed,  nor 
has  the  limit  to  their  size  and  power  yet  been  reached. 

Fig.  81  shows  several  Westinghouse  alternators  in 
position  at  a  water-power  station. 

The  electrical  engineer  usually  speaks  of  difference  of 
potential  as  electrical  pressure,  and  regards  the  two  factors 
of  electrical  energy  as  pressure  and  quantity  of  electricity. 
The  former  is,  in  effect,  the  driver  that  forces  the  current 
through  resistances  of  various  kinds,  and  the  latter  the 
quantity  of  electricity  which  passes  through  the  resistance. 
The  pressure,  quantity  of  electricity,  and  resistance  are  all 
measurable  quantities  and  have  their  proper  units  of 
measurement. 

The  Volt  is  the  unit  of  electrical  pressure  or  difference  of 
potential. 

The  Ohm  is  the  unit  of  electrical  resistance. 

The  Ampere  is  the  unit  of  current  strength,  and  is  defined 
as  the  current  that  passes  through  a  resistance  of  one  ohm 
under  a  pressure  of  one  volt. 

These  units  are  recognised  standards  of  measurement, 
and  are  just  as  well  defined  as  the  pound  and  the  foot  units 
of  weight  and  length. 

When  these  are  properly  correlated  they  may  be  put  into 
the  following  form  : — 

pressure  volts        n      V 

Current  =    r  .  ,      — ,  or  amperes  =  — -. ,  or  C  =  -=-> 

resistance  ohms  It 

This  relation  is  known  as  Ohm's  Law,  and  forms  the 
basis  of  a  large  number  of  electrical  calculations. 

The  energy  carried  by  a  current  is  directly  proportional 


ELECTRIC  SMELTING.  323 

to  the  pressure  and  to  the  current  strength,  and  when  it 
does  no  outside  work  is  entirely  converted  into  heat  which 
under  proper  conditions  can  be  used  as  such. 

The  Watt  is  the  unit  of  electrical  power  and  is  carried 
by  an  ampere  of  current ;  it  is  further  defined  by  introducing 
the  element  of  time.  The  watt  is  a  very  small  unit,  so  for 
practical  purposes  it  is  multiplied  by  1,000,  and  is  then 
known  as  the  Kilowatt. 

Joule  proved  that  one  watt- second,  that  is,  the  quantity 
of  energy  expended  in  one  second  by  one  ampere  of  current 
working  through  a  resistance  of  one  ohm  under  a  pressure 
of  one  volt,  develops  heat  sufficient  to  raise  3' 7  grains  of 
water  through  1°  C. 

He  also  proved  that  the  quantity  of  heat  required  to  raise 
1  Ib.  of  water  through  1°  C.  would,  if  expended  in  doing 
work,  raise  1,390  Ibs.  through  a  vertical  height  of  1  foot. 
Watt  estimated  that  a  horse  working  for  one  second  would 
raise  550  Ibs.  through  a  vertical  height  of  1  foot ;  and 
this  is  equivalent  to  raising  2,765  grains  of  water 
through  1°  C. 

Therefore  1  horse  power  =  —^-  =  746  watts. 

o"  i 

And  the  kilowatt  =  -=-rrr  —  1*34  h.  p. 

Value  of  746  watts  is  sometimes  called  the  electrical  horse- 
power— E.H.P.,  and  the  kilowatt-hour  is  the  Board  of  Trade 
unit  of  electrical  supply.  A  simple  calculation  shows  that 
8  kilowatt- hours  would,  if  converted  into  heat,  melt  1  cwt. 
of  cast  iron.  When  large  supplies  are  to  be  considered  the 
kilowatt-year  is  used,  and  this  is  usually  taken  as  365  X  24 
=  8,760  kilowatt-hours  ;  but  it  would  be  simpler  to  take 
10,000  for  this  large  unit.  The  cost  of  production  depends 
upon  a  number  of  circumstances,  among  which  the  cost  of 

Y  2 


324  IEON  AND   STEEL. 

the  mechanical  power  used  in  driving  the  dynamo  is  the 
most  important. 

One  of  the  first,  if  not  the  first,  applications  of  electricity 
to  the  treatment  of  iron  and  steel  was  made  by  Pepys  in 
1815,  when  he  split  a  piece  of  iron  wire,  filled  the  gap  with 
diamond  powder,  and  passed  a  powerful  current  through 
the  wire.  The  metal  was  thus  raised  to  a  bright  red  heat, 
and  in  six  minutes  the  diamond  dust  had  disappeared, 
while  the  iron  was  converted  into  "  blistered  steel."  The 
late  Sir  W.  Roberts-Austen  repeated  this  experiment  in  a 
vacuum  with  every  possible  precaution,  and  proved 
conclusively  that  red-hot  iron  will  absorb  solid  carbon. 

In  1849  Despretz  obtained  metallic  iron  from  a  mixture 
of  oxide  of  iron  and  carbon  by  the  heat  developed  with  an 
electric  current. 

In  1867  the  residual  magnetism  of  soft  iron  was  first 
taken  advantage  of  in  dynamo  construction,  and  the 
machine  was  thus  made  independent  of  everything  but  the 
power  required  to  drive  it.  Enormous  strides  have  been 
made  since  then,  and  now  the  only  limit  to  the  use  of 
electricity  in  iron  and  steel  manufacture  is  the  cost  of  the 
energy.  Much  has  been  done,  and  very  much  more 
attempted,  since  Siemens  introduced  his  small  electric  steel- 
melting  furnace  in  1879.  Only  the  more  successful  work 
can  be  referred  to  here. 

Electric  Furnaces  are  conveniently  classified  into  (i.)  arc 
furnaces,  (ii.)  resistance  furnaces,  (iii.)  induction  furnaces. 
They  all,  however,  depend  upon  the  heat  developed  by 
electrical  resistance. 

In  the  arc  furnace  the  heat  is  due  to  the  resistance  of 
gases  and  vapours,  and  in  the  resistance  furnace  to  that  of 
solid  and  liquid  bodies,  but  in  most  cases  there  is  also 
more  or  less  arcing  through  the  gaseous  matter  in  the 
furnace.  In  these  types  of  furnace  the  terminals  of  the 
generator  are  connected  by  leads  with  the  corresponding 


ELECTRIC  SMELTING.  325 

terminals  of  the  furnace,  so  that  in  the  empty  furnace  there 
is  a  gap  between  the  terminals,  and  no  current  can  pass. 
When  this  gap  is  bridged  over  by  conducting  matter  the 
current  passes,  and  its  energy  is  converted  into  heat.  The 
furnace  terminals  are  in  almost  all  cases  rods  or  blocks  of 
strongly  compressed  carbon,  and  when  these  are  brought 
together  and  then  separated,  an  arc  is  formed  between 
them  when  the  pressure  exceeds  40  volts.  The  arc  space 
absorbs  an  enormous  amount  of  energy  from  the  current 
with  the  development  of  a  correspondingly  high  temperature, 
and  it  is  probable  that  a  temperature  of  4,000°  C.  or  more 
has  been  obtained.  It  is  in  arc  furnaces  generally  that 
processes  requiring  exceptionally  high  temperatures  are 
carried  out.  Eesistance  furnaces  are  used  when  a  lower 
and  more  distributed  temperature  is  required. 

There  are  no  terminals  required  in  the  induction  furnace, 
as  it  is  based  upon  the  principle  of  the  transformer  used  in 
general  electrical  practice  for  reducing  the  pressure  of  high 
potential  currents.  To  understand  the  principle  involved, 
suppose  that  a  ring  of  soft  iron,  such  as  a  link  of  a  heavy 
cable,  has  a  coil  of  several  loops  of  insulated  copper  wire 
wrapped  round  one  part  of  it,  and  that  an  alternating 
current  is  passing  through  these  loops.  An  alternating 
magnetic  flux  is  set  up  in  the  soft  iron  corresponding  to  the 
alternations  of  the  current,  and  if  an  independent  coil  with 
a  smaller  number  of  loops  is  wrapped  round  another  part 
of  the  iron  ring,  alternating  currents  are  induced  in  this 
secondary  coil.  Now,  it  is  found  that,  neglecting  small 
losses,  the  average  pressure  of  the  current  in  the  secondary 
coil  is  reduced  in  the  same  proportion  as  the  number  of 
loops  in  the  coil  is  smaller  than  the  number  in  the  primary 
coil,  and  that  the  quantity  of  electricity  is  increased  in  the 
same  way.  Thus,  suppose  an  alternating  current  of  10 
amperes,  under  a  pressure  of  1,000  volts,  is  passing  through 
a  primary  coil  with  1,000  loops,  it  will  induce  a  current  of 


326  IRON  AND   STEEL. 

100  amperes  at  a  pressure  of  100  volts  in  a  secondary  coil 
consisting  of  10  loops,  and  with  one  loop  1,000  amperes  at 
10  volts.  These  heavy  currents  are  much  more  useful 
for  heating  and  lighting  purposes,  as  a  conductor  of  given 
cross-section  offers  more  resistance  to  their  passage.  High- 
potential  currents  are  usually  conveyed  over  long  distances 
by  comparatively  thin  conductors,  and  transformed  into  low- 
potential  currents  where  they  are  to  be  used.  Induction 
furnaces  are  in  effect  transformers  in  which  the  metal 
to  be  melted  is  made  to  take  the  place  of  the  secondary  coil. 

Steel  Making  in  the  Electric  Furnace. — It  is  improbable 
that  the  electric  furnace  will  be  able  to  compete  with  the 
Bessemer  and  open  hearth  processes  in  the  manufacture  of 
steel  for  constructional  purposes,  except  under  special 
conditions  ;  but  it  will  prove  a  serious  rival,  and  finally 
oust  the  old  processes  of  making  high-class  tool  steel.  Up 
to  the  present  the  electric  furnace  has  flourished  in  districts 
where  abundant  water  power  is  available;  but  with  the 
introduction  of  gas-driven  generators,  and  especially  where 
blast-furnace  gas  can  be  used,  it  is  sure  to  make  its  way 
into  the  iron  working  districts  of  this  country. 

The  Heroiilt  Process. — The  furnace  used  in  this  process 
is  of  the  resistance  type,  and  has  been  producing  high-class 
tool  steel  in  considerable  quantities  for  several  years  past. 
It  is  a  small  iron-clad  tilting  furnace,  lined  with  refractory 
material.  The  bed  plate  is  covered  with  a  layer  of  either 
dolomite  or  magnesite  bricks,  on  the  top  of  which  is 
rammed  the  working  bed  of  dolomite  lime.  The  roof  is 
lined  with  silica  bricks.  There  is  the  usual  spout  for 
pouring,  and  the  charging  door.  Two  massive  carbon 
blocks  are  suspended  side  by  side  through  two  openings  in 
the  roof,  but  out  of  contact  with  the  sides,  so  that  they  can 
be  moved  freely.  These  blocks  form  the  terminals  or 
electrodes  of  the  furnace,  and  are  so  arranged  that  they  can 
be  raised  or  lowered  separately,  either  by  hand  gearing 


ELECTRIC   SMELTING.  327 

or  by  small  motors  fixed  to  the  supports.  In  the  parts  of 
the  roof  between  the  electrodes  the  iron  plates  are 
replaced  by  bronze  to  prevent  the  forming  of  a  magnetic 
circuit  when  the  current  is  passing;  and  the  parts  of  the 


FIG.  82.— The  Heroult  Furnace. 
Furnace  lining.  F,  Tapping  spout. 


B,  ,,         roof. 

C,  Outlet  for  gases. 
7>,  Carbon  block. 


(7,  //,  Tilting  gear. 

M,  N,  Supports  for  carbons. 

K,  L,  Regulating  gear. 


electrodes  exposed  to  the  heat  of  the  roof  are  water- 
jacketed.  The  furnace  is  shown  in  section  in  Fig.  82. 

Steel  or  iron  scrap  of  average  quality,  such  as  crop  ends 
from  the  mill,  is  worked  into  high-class  tool  steel,  and  the 
operation  is  thus  described  : — 

The  scrap  is  charged  on  to  the  bed,  together  with  lime, 
and  the  electrodes  are  brought  down  so  as  to  touch  parts  of 
the  charge.  The  current  then  passes  from  one  electrode 


328  IKON  A^D   STEEL. 

to  the  other  through  the  charge.  A  number  of  arcs  are 
formed  by  the  imperfect  contact  at  various  points,  and 
heat  is  developed  due  to  the  resistance  of  the  charge 
generally.  During  the  melting  down  it  is  usual  to  switch 
out  the  motor  control  of  the  carbons,  and  regulate  them  by 
the  hand  gearing,  so  as  to  avoid  short-circuiting  as  much 
as  possible.  As  the  charge  melts  down  more  scrap  and 
lime  are  added,  and  when  it  is  quite  fluid  some  pure  ore  is 
thrown  in.  The  carbons  are  now  above  the  molten  bath, 
and  form  two  arcs  with  its  surface.  It  is  in  these  arcing 
spaces  that  most  of  the  heat  necessary  to  keep  the  bath 
molten  is  generated.  Slag  forms,  and  after  a  time  the 
furnace  is  tilted  to  run  it  off  as  completely  as  possible,  the 
last  portions  being  raked  off.  The  furnace  is  then  tilted  back, 
and  more  ore  and  lime  added  to  form  a  fresh  slag.  This  is 
poured,  and  a  third  slag  formed  in  the  same  way.  The 
removal  of  the  last  traces  of  impurity  is  thus  ensured. 
When  the  last  slag  has  been  run  off  the  metal  is  finished  in 
the  case  of  low  carbon  steel  by  the  addition  of  ferro- 
manganese,  and  for  high  carbon  steel  by  adding  a  calculated 
quantity  of  a  fritted  mixture  of  pure  iron  and  carbon, 
according  to  the  percentage  of  carbon  required  in  the 
finished  steel.  The  furnace  is  then  tilted  and  the  metal 
run  into  the  ladle  ready  for  casting. 

At  La  Praz,  in  the  South  of  France,  such  a  furnace  has 
been  at  work  for  several  years.  The  electrical  supply  is 
obtained  from  an  alternator  connected  directly  with  a  water 
wheel,  giving,  with  a  full  supply  of  water  to  the  wheel, 
4,000  amperes  at  a  pressure  of  110  volts.  This  is  equiva- 
lent to  590  h.p.,  and  in  working  for  tool  steel  as  much  as 
350  kilowatts  =  470  h.p.  were  being  absorbed  by  the 
furnace.  According  to  Harbord,  the  cost  of  the  electrical 
energy  is  7s.  Id.  per  ton  of  ingots  for  the  production 
of  2  tons  6  cwt.  of  steel  during  a  run  of  7  hours.  These 
figures  were  obtained  in  1904,  when  the  Canadian 


ELECTRIC  SMELTING. 


329 


as 


Commission   visited  La  Praz  with    Professor  Harbord 
its  metallurgical  expert. 

Dr.  Heroult  was  supplying  steel  to  the  Creusot  Works  as 
early  as  1900,  and  he  stated  that  hy  the  end  of  1904  the 
plant  in  operation  in  France  would  give  an  output  of  150 
tons  of  steel  per  day.  The  same  type  of  furnace  is  also  at 
work  in  Sweden  and  Germany.  In  the  last-named,  the 


FIG.  S3. — The  Heroult  Furnace  in  Position. 

electrical  energy  is  generated  by  the  use  of  blast-furnace 
gas  in  a  gas  engine. 

The  following  is  a  typical  analysis  of  the  tool  steel  made 
in  this  furnace  :— 

S  =  0-016  ;  P  =  0-006  ;  Si  =  0'02  ;  Mn  =  0'092  ;  C  =  T08 

The  carbon  may  be  varied  from  0*06  to  1*87  per  cent.  ; 
that  is,  various  grades  of  metal  from  the  softest  and  most 
ductile  iron  to  the  hardest  tool  steel  can  be  made  at  will.  A 
furnace  in  position  is  shown  in  Fig.  83. 

The  Kjcllin  Process. — The  furnace  used  in  this  process  is 
a  very  successful  example  of  the  application  of  the  principle 


330 


IRON  AND   STEEL. 


of  induction  to  either  a  melting  or  a  smelting  process. 
The  body  of  the  furnace  is  built  of  ordinary  furnace 
masonry  and  may  be  either  circular  or  rectangular  in  cross 
section.  Looked  at  from  above,  the  hearth  or  crucible  is 
seen  to  consist  of  a  ring-like  space  in  the  masonry,  lined 
with  either  acid  or  basic  refractory  material,  and  fitted  with 
a  movable  cover  made  in  segments  so  that  parts  of  it  can 


FIG.  84.— The  Kjellin  Furnace. 

A,  Primary  coil.  F,  Air  chamber. 

B,  Furnace  hearth.  (7,  Exhaust  pipe. 
0,  Iron  core.                                         //,  Tap  hole. 

D,  E,  Masonry.  K,  Covers. 

be  taken  off  as  required.  This  ring  hearth  is  nearer  to  one 
side  of  the  structure,  and  the  tap  hole  leads  from  this  near 
part  of  the  hearth  to  a  spout  fixed  to  the  outside  wall. 
Inside  the  hearth  ring  and  concentric  with  it  is  a  circular 
space  separated  from  the  hearth  by  a  thick  ring  of  firebrick. 
In  the  centre  of  this  space  is  a  laminated  core  made  up  of  soft 
iron  plates,  and  surrounded  by  a  coil  of  insulated  copper 
wire  of  many  turns.  The  core  is  continued  horizontally 
above  and  below7  to  a  second  piece  let  into  the  masonry 


ELECTRIC   SMELTING.  331 

outside  the  hearth  space.  The  whole  thus  forms  a  closed 
magnetic  circuit  similar  to  the  cable  link  referred  to  on 
p.  325.  The  space  containing  the  coil  is  closed  in  at  the 
top  and  connected  with  a  pipe  by  which  a  rapid  current  of 
cold  air  can  be  drawn  through  to  keep  it  cool  when  the 
furnace  is  working.  The  ends  of  the  coil  are  connected  by 
leads  with  the  terminals  of  an  alternator  driven  by  a  water 
turbine,  and  capable  of  supplying  a  current  of  from  80  to 
90  amperes  at  a  pressure  of  3,000  volts.  Fig.  84  shows 
the  furnace  in  vertical  section.  To  work  the  furnace 
sufficient  molten  pig  iron  is  run  into  the  hearth  to  form  a 
molten  ring  of  metal  round  it.  The  furnace  is  now  a 
transformer,  for  the  ring  of  metal  forms  the  secondary 
circuit,  and  when  the  current  is  switched  on  the  transforming 
commences.  The  number  of  loops  in  the  primary  coil  is 
such  that  an  induced  current  of  30,000  amperes  at  a 
pressure  of  7  volts  is  set  up  in  the  molten  circuit,  and 
much  heat  is  generated.  The  full  charge  is  then  made  up 
by  the  addition  of  charcoal  iron  and  scrap  from  time  to 
time  until  the  whole  is  melted.  It  is  then  kept  in  the 
furnace  for  a  time  for  the  temperature  to  rise  sufficiently 
for  tapping,  when  about  two-thirds  is  run  into  the  casting 
ladle,  and  cast  into  ingots.  The  remainder  is  left  in  the 
hearth  to  continue  the  transforming,  and  the  full  charge  is 
made  up  and  worked  through  in  the  same  manner. 

The  process  has  been  in  use  at  Gysinge  Bruk  in  Sweden 
since  1900  under  the  supervision  of  Mr.  Kjellin,  and  is 
without  doubt  a  success  there ;  but  it  seems  to  be  specially 
adapted  to  the  treatment  of  the  very  pure  materials  peculiar 
to  the  district.  Very  little  refining  goes  on,  and  except  for 
the  oxidation  of  a  small  portion  of  the  carbon  and  iron,  the 
action  is  a  pure  melting  one.  It  is,  therefore,  possible  to 
arrange  a  charge  of  pure  pig  iron,  wrought  iron,  and  scrap 
of  known  composition  to  produce  steal  of  a  given  composi- 
tion. Additions  of  ferro-manganese  and  other  iron  alloys 


332 


IKON  AND   STEEL. 


may  be  made  for  the  production  of  special  steels.  Somewhat 
recently  pig  and  ore  have  been  used  in  place  of  pig  and 
scrap,  but  this  reduces  the  output,  and  very  pure  ore  must 
be  used  if  the  product  is  to  be  high  class.  One  of  the 
recent  furnaces  is  12  feet  in  diameter,  8  feet  high,  and 
has  a  capacity  of  35  cwt.  The  energy  absorbed  is  about 
240  h.p.  and  the  output  5  to  5J  tons  per  24  hours.  About 
6  hours  is  required  to  work  off  a  charge  of  25  cwt.  But 


FIG.  So. — The  Stassano  Furnace. 

two  larger  furnaces  of  1,000  h.p.,  of  which  the  dimensions 
are  not  to  hand,  are  now  at  work. 

The  following  analysis  is  given  by  Mr.  Eitchie,  of  Glasgow, 
who  saw  the  process  in  operation,  and  analysed  samples  of 
the  steel  :— 

S  =  0-012  ;  P  =  0-015  ;  Si  =  0'093  ;  Mn  =  0'044  ;  C  =  1'33. 

The  use  of  aluminium  for  the  reduction  of  pure  oxide  of 
iron  in  a  furnace  of  this  type  should  solve  the  problem  of 
obtaining  carbonless  iron  for  experimental  purposes.  A 
small  induction  furnace  with  a  basic  lined  hearth  of  a  few 
pounds  capacity  would  furnish  either  the  pure  metal  or 


ELECTEIC   SMELTING.  333 

alloys  of  controlled  composition,  and  the  questionable 
method  now  in  use  of  determining  the  influence  of  a  particular 
element  on  the  physical  and  mechanical  properties  of  iron 
in  the  presence  of  other  elements,  would  be  avoided. 

The  Stassano  Process. — The  latest  form  of  furnace,  used 
by  Major  Stassano  in  carrying  out  his  process,  is  of  the  arc 
type  pure  and  simple.  It  consists  of  a  circular  chamber 
about  3  feet  3  inches  in  diameter  and  of  the  same  height.  It 
is  lined  with  refractory  brickwork,  and  has  a  dome  roof.  The 
carbon  electrodes,  A,  which  are  about  9  inches  in  diameter, 
enter  the  chamber  through  openings  midway  between  the 
floor  and  the  roof.  They  are  fitted  with  regulating  gear  by 
which  they  can  be  caused  to  meet  in  the  centre  of  the 
chamber,  or  their  free  ends  may  be  brought  flush  with  the 
walls.  There  are  tap  holes  for  the  metal  and  the  slag,  one 
near  the  bottom  of  the  hearth,  and  the  other  midway 
between  the  bottom  and  the  electrode  openings.  The  parts 
of  the  electrodes  outside  the  chamber  are  water  jacketed  to 
keep  them  cool.  The  furnace  is  iron  clad,  and  is  fixed  at 
the  bottom  to  a  shaft  slightly  inclined  to  the  vertical,  by 
which  it  can  be  rotated  on  bearings  at  the  rate  of  one  to 
two  revolutions  per  minute.  In  this  way  the  charge  may  be 
set  in  motion  and  the  tap  hole  brought  to  the  lowest 
position  when  tapping.  The  charge  is  put  into  the  furnace 
through  an  inclined  shoot  in  the  side. 

As  the  furnace  is  revolving  while  the  current  is  passing, 
the  carbon  electrodes  are  connected  with  the  fixed  leads 
from  the  generator  by  a  rubbing  contact  at  C.  To  effect  this 
two  fixed  insulated  rings  are  provided  upon  which  contact 
pieces  connected  with  the  electrodes  are  pressed  during  the 
rotation  of  the  furnace.  The  furnace  that  has  given  the 
greatest  satisfaction  is  one  of  200  h.p.  and  this  absorbs 
about  140  kilowatts.  The  current  is  furnished  by  a  water 
driven  alternator.  The  form  of  the  furnace  is  shown  in 
vertical  section  in  Fig.  85.  A  200  h.p.  furnace  at  work  in 


334  IRON  AND   STEEL. 

the  Artillery  Construction  Works,  Turin,  for  the  Italian 
Government  produces  steel  for  artillery  projectiles  from  the 
following  materials  in  regulated  proportions :  (i.)  pig  iron 
turnings  with  sufficient  ore  and  lime  for  refining  the  metal 
and  slagging  the  impurities  ;  (ii.)  iron  and  steel  turnings  ; 
(iii.)  iron  and  steel  scrap  ;  (iv.)  ferro-silicon  and  ferro-man- 
ganese  for  deoxidation  and  introduction  of  sufficient  man- 
ganese into  the  finished  steel.  The  product  contains  :— 

P  =  0-03  to  0-04 ;  C  =  0'3  to  0'4  ;  Mn  =  1-2  to  1-5. 

Very  little  loss  of  metal  occurs,  and  the  electrodes  lose 
about  10  Ib.  per  ton  of  steel.  According  to  the  inventor,  it 
will  make  other  varieties  of  steel  either  soft  or  hard  just  as 
readily  by  properly  regulating  the  charge.  There  is  no 
doubt  that  the  furnace  will  make  steel  successfully.  One 
of  its  advantages  is  that  the  electrodes  are  kept  clear  of  the 
bath  so  that  contamination  of  the  metal  from  that  source 
is  not  possible.  One  of  its  disadvantages  is  in  the  removal 
of  the  slag ;  but  Stassano  says  that  it  can  be  completely 
removed  in  actual  working. 

The  Stassano  Electric  Furnace  Company  of  Turin  have 
lately  installed  three  furnaces,  one  of  1,000  h.p.  with  three 
pairs  of  electrodes,  one  of  200  h.p.  and  one  of  100  h.p., 
but  no  details  of  their  working  are  yet  published. 

The  Electric  Smelting  of  Iron  Alloys. — The  preparation 
of  iron  alloys  in  the  electric  furnace  is  of  the  most  general 
importance,  for  in  several  cases  they  are  either  very 
difficult  to  produce  or  cannot  be  produced  in  an  ordinary 
furnace.  In  fact,  some  of  them  owe  their  existence  com- 
mercially to  the  electric  furnace.  Alloys  of  iron  with 
silicon,  manganese,  aluminium,  nickel,  chromium,  tungsten, 
titanium,  molybdenum,  and  vanadium  are  now  in  common 
use ;  and  although  some  of  them  are  made  extensively  in 
the  blast  furnace,  it  is  probable  that  eventually  they  will 
be  almost  entirely  produced  in  the  electric  furnace.  Many 


ELECTEIC  SMELTING.  335 

inventors  have  applied  their  energies  in  this  direction,  and 
some  so  successfully  that  it  would  be  somewhat  invidious 
to  select  any  one  for  first  place,  but  M.  Keller  of  the  Keller, 
Leleux  Company,  Livet,  France,  has  done  much  in  this 
direction ;  and  Mr.  A.  J.  Eossi  has  been  a  most  successful 
pioneer  of  the  industry  in  America. 

The  production  of  ferro-alloys  depends  entirely  upon  the 
reduction  of  the  oxide  of  the  second  element  in  the  alloy  by 
carbon  in  the  presence  of  either  metallic  iron  or  its  oxide, 
which  is  then  reduced  simultaneously.  It  is  well  known 
that  when  the  reduction  is  effected  by  carbonaceous  matter, 
or  in  the  presence  of  the  same,  carbon  itself  is  absorbed  by 
the  alloy.  In  this  way  as  much  as  8  per  cent,  of  the 
element  may  be  associated  with  the  metals.  This  may  or 
may  not  be  a  drawback,  depending  upon  the  purpose  to 
which  the  alloy  is  to  be  put.  It  is  possible,  however,  to 
considerably  reduce  the  amount  of  carbon  in  the  final 
product. 

Mr.  Rossi  is  especially  interested  in  the  production  of 
ferro-titaniom,  the  effects  of  which  upon  the  transverse  and 
tensile  strength  of  cast  iron  and  steel  are  remarkable.  He 
claims  an  increase  of  20  to  25  per  cent,  in  the  transverse 
and  20  to  30  per  cent,  to  the  tensile  strength  of  cast  iron 
by  the  addition  of  0*1  per  cent,  of  titanium  to  the  bath  of 
molten  metal  before  casting.  It  also  increases  the  elastic 
limit  of  steel.  The  effect  is  probably  due  to  the  expulsion 
of  occluded  gases,  and  the  closing  up  of  the  grain  of  the 
metal. 

Rossi's  furnace,  which  is  square  in  section,  consists 
essentially  of  a  graphite  crucible  with  a  tap  hole  leading 
from  the  bottom.  The  crucible  itself  is  connected  by  a  bus- 
bar with  the  electric  supply,  and  thus  forms  one  of  the 
electrodes.  The  other  electrode  is  a  carbon  block  suspended 
within  the  crucible,  so  that  it  can  be  raised  and  lowered  by 
mechanism  above.  Such  a  furnace  3^  feet  high  and  4  feet 


336  IRON  AND   STEEL. 

square  will  absorb  150  kilowatts  at  a  pressure  of  from  20  to 
100  volts.  The  shell  of  the  furnace  is  made  of  iron  plates, 
and  is  lined  with  graphitic  material. 

The  smelting  mixture  for  ferro-chromium  consists  of 
chrome  iron  ore  and  carbon,  and  is  fed  in  at  the  top.  The 
arc  is  struck  by  lowering  the  electrode  to  make  contact  and 
then  raising  it  again.  The  charge  is  added  at  intervals, 
and  when  sufficient  metal  has  collected  it  is  tapped  out. 
Any  slag  that  may  collect  is  run  away  by  another  opening, 
the  charging  is  continued,  and  more  metal  collects.  The 
process  is  practically  a  continuous  one.  The  richness  of 
the  alloy  depends  upon  the  proportions  of  the  mixture. 
Thus  if  chromium  oxide  only  is  used,  chromium  free  from  iron 
is  obtained.  Kossi  makes  ferro-chromium  containing  up  to 
78  per  cent,  of  chromium,  and  from  6  to  7  per  cent,  of 
carbon ;  but  he  is  able  to  remove  the  greater  part  of  the 
carbon  by  the  addition  of  oxides  to  the  furnace  before  the 
metal  is  tapped.  A  very  oxidising  slag  is  thus  formed,  and 
much  of  the  carbon  is  oxidised  and  removed.  The  lower 
limit,  however,  appears  to  be  from  1  to  2  per  cent,  carbon. 

But  alloys  practically  free  from  carbon  can  be  obtained 
by  using  a  bath  of  aluminium  for  the  reducing  agent.  Scrap 
aluminium  is  melted  in  the  furnace,  and  the  oxides  added 
carefully  on  account  of  the  great  heat  developed  by  the 
reduction.  The  whole  of  the  aluminium  may  be  oxidised, 
and  thus  prevented  from  contaminating  the  metal  by  the 
addition  of  sufficient  oxide,  and  the  judicious  use  of  the 
current.  The  change  is  expressed  thus  : — 

Cr203  +  2  Al  -  A1203  +  2  Cr. 

Chromic  Oxide.  Slag. 

The  metal  is  tapped  in  the  usual  manner,  and  is  found  to 
contain  very  little  carbon,  but  is  not  free  from  that  element, 
as  it  is  in  contact  with  the  carbon  walls  of  the  crucible.  A 
better  method  would  be  to  use  a  furnace  of  the  Kjellin 


ELECTRIC   SMELTING. 


337 


type.     The  aluminium  could  then  be  melted,  and  the  oxides 
reduced  without  any  risk  of  contamination  with  carbon. 

The  Keller  Furnace  is  more  complicated  than  the  one 
described  above,  and  for  some  purposes  more  efficient.  It 
consists  of  a  number  of  hearths  connected  together,  and 
capable  of  being  worked  together.  In  the  vertical  section, 
Fig.  86,  two  vat-shaped 
hearths  are  shown  con- 
nected together  by  a 
central  well,  in  which 
the  reduced  metal  or 
alloy  collects  together 
with  any  slag  that  may 
form.  The  carbon  elec- 
trodes A,  B,  which  are 
connected  with  the  alter- 
nator, serve  for  the  pas- 
sage of  the  current  into 
and  out  of  the  furnace. 
The  smelting  mixture  is 
fed  into  the  top  of  each 
hearth,  and  gradually 
works  down  as  it  is  re- 
duced. The  circuit  is 
made  by  the  two  elec- 

trodes  and  the  material  Fl(J  g6  _The  Kel,el.  Pumace_ 

between  them,  and  the 

heat  is  furnished  by  the  resistance  of  the  latter  as  the 
current  passes  to  and  fro  in  it.  The  central  electrode 
C  is  for  heating  the  contents  of  the  well  should  the  tempera- 
ture fall  too  low.  It  can  be  put  into  use  at  any  time  by 
lowering,  and  then  raising  it  so  as  to  form  an  arc  with  the 
contents  of  the  well.  When  the  metal  is  tapped  the  level 
falls,  and  the  circuit  is  more  or  less  broken.  This  interferes 
not  only  with  the  working  of  the  furnace,  but  also  with 
i.s.  z 


338  IRON  AND   STEEL. 

that  of  the  alternator,  which  is  bad  for  both.  To  obviate 
this  carbon  blocks  are  built  into  the  bottom  of  each  hearth, 
and  are  connected  together  by  copper  rods,  which  gradually 
take  up  part  of  the  load  as  the  level  of  the  metal  sinks  in 
the  well.  As  the  level  of  the  metal  rises  again  they  are 
gradually  put  out  of  action,  and  the  load  taken  on  by  the 
furnace  charge. 

One  important  feature  of  this  furnace  is  that  the  products 
of  reduction  are  removed  from  the  zone  of  highest 
temperature  as  they  form,  and  collect  in  the  well.  This 
proves  very  useful  in  the  production  of  ferro- silicon. 

Ferro-Silicon. — The  melting  charge  used  by  Keller  for 
the  production  of  this  useful  alloy  consists  of  crushed 
quartz,  scrap  iron,  and  coke.  The  silica  is  reduced  by 
carbon  in  the  presence  of  iron,  and  the  silicon  passes  into 
the  metal.  In  the  reduction  of  silica  by  carbon  there  is  a 
tendency  for  the  reduced  silicon  to  unite  with  carbon  to  form 
the  carbide  known  as  carborundum,  and  this  tendency 
increases  as  the  temperature  rises,  but  it  is  found  that  the 
rapid  removal  of  the  silicon  from  the  zone  of  highest 
temperature  enables  the  nearly  pure  element  to  be  obtained, 
and  very  little  reaction  with  carbon  takes  place.  Thus 
ferro-silicons  containing  up  to  98  per  cent,  silicon  are  by 
no  means  rare,  but  the  poorer  varieties  are  mostly  produced. 
There  is  a  tendency  for  the  rich  alloys  to  disintegrate  on 
exposure  to  the  air,  and  this  is  not  in  their  favour.  Keller 
states  that  with  electric  energy  equal  to  10,000  h.p.  he 
could  produce  30  tons  of  30  per  cent,  ferro-silicon  per 
day. 

The  tungsten,  molybdenum,  vanadium  alloys  are  prepared 
in  a  similar  mariner  by  smelting  their  oxides  with  iron 
oxide,  or  iron-producing  material  and  carbon.  The  oxides 
are  prepared  in  a  fairly  pure  condition  by  taking  advantage 
of  the  fact  that  they  combine  with  the  alkaline  oxides,  soda 
and  potash,  to  form  soluble  compounds.  The  ores  of  the 


ELECTRIC  SMELTING.  339 

metals  are  concentrated  as  far  as  possible  by  crushing  and 
washing,  and  then  roasted  with  free  access  of  air  to  remove 
volatile  bodies,  such  as  sulphur  and  arsenic.  The  roasted 
product  is  then  melted  with  carbonate  of  soda.  The  mass 
is  crashed  and  treated  with  water  to  dissolve  out  the 
soluble  matter,  which  contains  the  oxide  of  the  metal  under 
treatment.  The  solution  is  acidified  with  sulphuric  acid, 
which  takes  up  the  soda  and  precipitates  the  oxide.  This 
is  then  collected  and  dried,  when  it  is  ready  for  the  electric 
furnace.  When  a  reducible  metal,  such  as  lead  in  vanadate 
of  lead,  is  present,  coal  is  added  in  addition  to  the  carbonate 
of  soda  for  the  smelting,  and  the  lead  is  obtained  in  the 
metallic  state.  The  alloys  of  these  metals  are  of  great 
importance,  as  they  are  used  in  the  manufacture  of  special 
steels.  (See  Chap.  XIV). 

Electric  smelting  has  been  carried  on  in  Canada,  but  is 
more  or  less  in  the  experimental  stage,  although  it  is  proved 
that  the  processes  can  be  made  commercially  successful. 
It  is  largely  the  outcome  of  the  visit  of  a  Government 
Commission  to  Europe  some  three  years  ago  to  investigate 
these  smelting  processes  generally. 

In  1904  Mr.  E.  A.  Sjostedt,  of  Sault  Ste.  Marie,  Ontario, 
conducted  some  very  successful  experiments  for  the  pro- 
duction of  ferro-nickel  from  a  nickeliferous  pyrites.  The 
ore  was  roasted  down  to  3  per  cent,  of  sulphur  and  then 
smelted  in  admixture  with  lime  and  ground  coke  in  a 
rectangular  furnace  lined  with  magnesite  bricks.  The  lower 
electrode  consisted  of  a  thick  carbon  rod  running  the  full 
length  of  the  bottom,  and  the  upper  electrode  of  a  number 
of  rods  arranged  in  a  row  directly  over  the  lower  one.  The 
furnace  was  worked  with  1,350  amperes  at  a  pressure  of 
80  volts,  or  108  kilowatts,  and  had  an  output  of  13  cwts.  of 
the  alloy  per  24  hours.  The  slag  notch  and  tap  hole  were 
at  opposite  ends  of  the  furnace. 

Dr.  Haanel  also  conducted  some  experiments  at  Sault  Ste. 

z  2 


340  IRON  AND  STEEL. 

Marie  in  1906  under  Government  auspices.  The  chief 
object  of  these  experiments  was  to  prove  whether  the 
principal  Canadian  ore,  magnetite,  could  be  successfully 
treated  in  the  electric  furnace,  and  whether  roasted  iron 
pyrites  could  be  smelted  for  the  production  of  pig  iron 
practically  free  from  sulphur.  The  conditions  are  :  abund- 
ance of  ore,  wood  for  charcoal,  and  water  power. 

The  furnace  used  is  circular  in  section,  and  consists  of 
of  an  iron  shell  the  bottom  of  which  is  lined  with  a  thick 
hollo  wed-out  block  of  compressed  carbon  to  form  the  hearth, 
and  the  sides  with  firebricks.  The  internal  dimensions 
are  3  feet  9  inches  deep  and  2  feet  9  inches  wide.  The 
hearth  serves  as  the  lower  electrode,  and  the  upper  electrode 
consists  of  a  carbon  block  so  suspended  that  it  can  be 
raised  or  lowered  in  the  furnace  at  will.  The  shell  is  made 
in  two  semi-circular  parts  which  are  joined  together  by 
copper  strips.  This  prevents  the  formation  of  a  magnetic 
circuit  with  its  consequent  loss  of  energy.  The  current  is 
furnished  by  a  water-driven  alternator  at  2,400  volts,  and 
reduced  to  50  volts  by  a  transformer.  The  energy  absorbed 
by  the  furnace  when  working  is  about  230  e.h.p.  Accurate 
measuring  instruments  were  used  in  the  experimental  runs, 
and  every  precaution  taken  to  determine  the  actual  cost  of 
working. 

The  charge  consisted  of  ore,  charcoal,  and  flux,  the  nature 
of  the  latter  depending  upon  the  gangue  to  be  removed. 
Limestone  is  the  common  flux,  but  sand  is  sometimes 
required. 

The  composition  of  samples  of  the  pig  iron  and  slag  is 
shown  by  the  table  on  the  next  page. 

Carbon  monoxide  is  formed  during  the  reduction,  and 
attempts  were  made  to  utilise  it  for  pre-heating  the  charge 
in  the  furnace,  but  with  indifferent  success.  There  is  no 
doubt,  however,  that  it  could  be  drawn  off  and  used  for 
heating  purposes  outside  the  furnace  itself.  The  tests 


ELECTRIC  SMELTING. 


341 


were  so  satisfactory  that  a  larger  and  more  complete  plant 
should  have  a  successful  career. 

Smelting  Ores. — In  Brazil  a  high  grade  ore  can  be 
delivered  near  a  water-power  station  at  10s.  6d.  per  ton, 
and  mild  steel  can  be  produced  from  it  at  a  cost  of  6s. 
per  ton  for  electrical  energy.  The  price  of  coke  in  the 
district  is  48s.  per  ton,  and  there  is  a  prohibitive  tariff  on 
imported  iron.  A  smelting  plant  at  this  place  should 
clearly  be  a  huge  success. 

There  is  not  the  slightest  difficulty  in  the  reduction  of 
iron  ores  in  the  electric  furnace.  It  is  simply  a  matter  of 


Grey  Pig  Iron. 

Slag. 

Carbon 

.     4-65 

Silica 

.     35-84 

Silicon 

.     1-41 

Alumina  . 

.     31-80 

Phosphorus 
Sulphur    . 

.     G'012 
.     0-024 

Lime 
Magnesia  . 

.     14-39 
.     16-22 

Sulphur    . 

.       0-26 

Iron  . 

.       0-35 

cost,  and  it  would  appear  that  it  is  only  in  special  cases 
that  the  electric  furnace  could  possibly  compete  with 
the  modern  blast  furnace.  For  refining  processes  on  the 
large  scale  in  the  open  hearth  it  is  simply  the  question  of 
price  of  electrical  energy  against  the  price  of  producer  gas, 
for  little  difficulty  would  be  encountered  in  the  electrical 
heating  of  furnaces  of  50  tons  capacity  and  upwards.  But 
it  is  in  the  use  of  blast  furnace  gas  as  a  source  of  electrical 
energy  for  the  production  of  high  grade  steel  and  ferro- 
alloys, that  the  first  advances  will  be  made  away  from  the 
water  power  districts. 

Heroult,  Keller,  Stassano,  Gin,  and  others  have  proved 
the  practicability  of  obtaining  either  pig  or  refined  metal 
direct  from  the  ore  by  electrical  heating,  but  at  present  their 


342  IRON  AND   STEEL. 

apparatus  is  more  economically  engaged  in  the  production 
of  high  grade  steel  and  ferro-alloys.  Keller's  experiments 
lead  to  the  conclusion  that  the  ore  can  he  smelted,  the  pig 
refined,  and  the  ingots  reheated  for  the  mill.  For  the 
carbon  monoxide  liberated  during  the  reduction  of  the  ore 
is  sufficient  to  work  a  reheating  furnace. 

In  districts  where  water  power  is  not  available,  but  where 
supplies  of  raw  materials  and  fuel  can  be  readily  obtained, 
the  ideal  iron  and  steel  works  should  be  self-contained. 
Take  a  case  with  which  the  writer  is  acquainted.  After 
the  expenditure  of  much  labour  and  capital,  blast  furnace 
gas  is  being  used  direct  in  gas  engines,  and  about  4,000  h.p. 
is  being  so  developed.  Now,  what  is  to  prevent  the  instal- 
lation of  say  the  Heroult  and  Keller  processes  for  the 
production  of  high  grade  steel  and  ferro-alloys  in  this  and 
similar  works  ?  It  will  come  in  time,  and  it  is  to  be  hoped 
that  some  at  least  of  the  pioneer  work  will  be  done  in  this 
country,  and  not  left  to  Germany  and  America. 

Electric  welding  forms  part  of  the  electrical  treatment 
of  metals,  and  may  be  effected  by  either  "  arc "  or 
"  resistance"  heating.  In  welding  by  the  arc  the  work  is 
connected  with  the  positive  lead  and  thus  forms  the 
positive  electrode,  while  the  negative  electrode,  a  carbon 
rod,  is  held  by  the  workman.  With  a  pressure  of  110 
volts  and  a  good  supply  an  arc  two  inches  long  is  formed 
between  the  work  and  the  carbon,  so  that  the  metal  is 
rapidly  softened,  and  can  then  be  worked  together  by  a 
former.  Flanges  are  welded  on  to  solid  drawn  steel  tubes 
by  this  method.  Resistance  welding  machines  are  trans- 
formers in  principle,  in  which  heavy  alternating  currents 
of  low  pressure  pass  through  the  junction  of  the  pieces  to 
be  welded,  and  the  heat  generated  there  softens  the  metal, 
while  the  machine  exerts  the  necessary  pressure  to  effect 
the  weld.  Tramway  rails  are  sometimes  welded  together 
in  this  way. 


CHAPTER  XIV. 

SPECIAL    STEELS. 

THE  rapid  increase  in  the  world's  output  of  iron  and  steel 
and  their  very  much  extended  use  for  a  variety  of  purposes, 
evidently  demanded  more  rapid  methods  of  dealing  with 
large  pieces  in  the  finishing  processes.  Both  forgings  and 
castings  have  to  be  turned,  planed,  and  milled  in  a  variety 
of  ways,  and  an  increase  in  the  rate  at  which  they  can  be 
dealt  with  on  the  lathe  or  machine  is  of  considerable 
importance. 

One  of  the  principal  difficulties  in  the  way  of  rapid 
working  with  ordinary  carbon  steel  tools,  is  due  to  the  rapid 
conversion  of  mechanical  energy  into  heat.  This  develop- 
ment of  heat  takes  place  near  to  the  cutting  edge  where  the 
work  is  being  done,  and  if  it  goes  on  too  rapidly  the  tool 
may  be  raised  to  a  temperature  above  that  at  which  its 
hardening  carbon  passes  into  the  cement  form.  This 
would  soon  soften  the  tool,  and  put  it  out  of  action.  The 
tool  may  be  flooded  with  some  cooling  liquid  while  it  is  at 
work,  but  even  then  the  speed  limit  appears  to  be  only 
30  to  50  feet  per  minute. 

Self -hardening  Steels. — The  first  step  in  the  direction  of 
increasing  the  speed  of  working  was  made  by  R.  Mushet, 
in  1868,  when  he  introduced  the  self-hardening  steel  known 
by  his  name.  This  steel  is  an  iron-manganese-tungsten 
alloy,  which  did  not  receive  the  attention  it  deserved,  as  all 
its  properties  were  not  understood,  even  by  Mushet  himself. 
It  should  be  mentioned,  however,  that  Mr.  Jacobs  and  Dr. 
Koeller,  in  1855,  drew  attention  to  the  effect  of  tungsten  in 


344 


IRON  AND  STEEL. 


closing  the  grain  of  steel  and  rendering  its  fracture  silky. 
The  steel,  as  made  by  Mushet,  has  been  largely  used  in  the 
working  of  hard  metals  on  account  of  its  increased  hardness 
and  resistance  to  shearing  stress.  By  self-hardening,  it  is 
meant  that  the  steel  may  be  made  to  sustain  a  cutting  edge 
by  proper  heat  treatment  without  the  quenching  necessary 
for  carbon  steel.  Thus,  if  a  tool  is  raised  to  a  medium 
orange  heat,  and  then  allowed  to  cool  naturally,  it  is  ready 
for  use.  The  important  function  of  the  tungsten  is  to  keep 
the  carbon  in  the  hardening  form  at  a  comparatively  high 
temperature,  and  so  prevent  softening,  while  the  self- 
hardening  property  appears  to  be  due  almost  entirely  to 
the  presence  of  sufficient  manganese.  In  the  absence  of  this 
element  the  tungsten-carbon-iron  alloy  has  little  or  no  self- 
hardening  properties,  but  requires  to  be  quenched  in  the 
ordinary  way.  Oil  or  water  hardening,  however,  renders 
these  steels  excessively  hard  and  brittle,  so  that  even  if 
they  do  not  crack  in  the  process,  they  are  practically 
useless.  The  method  of  annealing  them  is  to  heat  to  a 
bright  red  heat  for  about  24  hours,  and  then  cool  slowly  in 
hot  sand  or  ashes.  Some  brands  can  be  annealed  by 
heating  to  a  dull  red  heat,  and  then  quenching  in  water. 
This  is  remarkable,  but  at  the  same  time  effective.  The 
composition  of  some  of  these  alloys  is  given  in  the  following 
table  :— 

SELF-HARDENING  on  MUSHET  STEELS. 


Carbon 

1-67 

2-30 

2-05 

2-00 

2-35 

Silicon 

0-38 

1-05 

0-79 

1-60 

0-15 

Manganese  . 

2-53 

2-57 

2-30 

1-72 

3-38 

Tungsten     . 

5-47 

6-12 

8-04 

8-22 

11-02 

Phosphorus 

0-04 

0-04 

Sulphur 

0-04 

0-02 

When  the  tungsten  does  not  exceed  3*5  per  cent.,  and  the 
manganese  0'5  per  cent.,  with  low  silicon,  the  steel  can  be 


SPECIAL  STEELS.  345 

hardened  by  water-quenching  in  the  usual  manner.  But 
such  steels  are  expensive,  and  do  not  possess  any  particular 
advantage  over  good  carbon  steel.  Chromium  in  small 
quantity  is  also  found  in  some  varieties  of  self-hardening 
steels. 

The  proper  heat  treatment  of  carbon  steel  is  most 
important,  for  comparatively  slight  over-heating  deteriorates 
the  metal,  and  the  higher  the  carbon  the  greater  the  care 
required.  This  was  thought  to  be  true  also  of  the  tungsten 
alloys,  but  Messrs.  Taylor  and  White  made  a  most 
important  step  forward  when  they  proved  that  steel 
containing  tungsten  could  be  heated  near  its  melting  point 
and  then  quenched  in  a  blast  of  air  without  deterioration. 
Further,  that  a  tool  treated  in  this  way  could  be  worked  at 
a  higher  speed  without  softening.  In  fact,  such  a  tool  can 
be  worked  at  a  temperature  that  would  render  ordinary 
steel  perfectly  useless.  It  is  said  to  be  "  red  hard,"  that 
is,  it  retains  its  normal  hardness  at  a  red  heat.  The 
cutting  speed  can  thus  be  increased  up  to  500  feet  per 
minute  if  necessary,  but  the  usual  speeds  are  much  less 
than  this,  or  about  150  feet  per  minute.  The  Bethlehem 
Steel  Companj7  gave  a  demonstration  of  high  speed  turning 
at  the  Paris  Exhibition  of  1900,  and  since  then  many  steel 
makers  have  turned  their  attention  to  this  most  important 
subject.  Mr.  J.  M.  Gledhill,  of  Messrs.  Armstrong, 
Whitworth  and  Company,  has  investigated  the  composition 
and  properties  of  these  alloys,  and  the  "  A.W."  high-speed 
steel,  manufactured  by  the  company,  is  justly  celebrated. 
The  elements  so  far  used  in  the  production  of  these  steels 
are  tungsten,  chromium,  molybdenum,  and  vanadium, 
together  with  the  elements  usually  present  in  ordinary 
steel,  and  some  of  these  alloys  contain  as  much  as  30  per 
cent,  of  matter  other  than  iron.  Mr.  Gledhill  states  that 
the  alloys  are  best  made  from  cemented  Swedish  bar,  and 
this  is  the  orthodox  method  in  this  country  for  producing 


346  IRON   AND   STEEL. 

the  best  brands.  American  authorities,  however,  are  of 
opinion  that  any  equally  pure,  uncemented  bar  can  be  used, 
and  much  of  the  American  high  speed  steel  is  quite  innocent 
of  anything  Swedish.  The  principal  reason  for  the  use  of 
Swedish  iron  in  this  country  is  that  much  of  our  own  marked 
bar  is  hardly  pure  enough  for  the  purpose ;  but  it  is  said 
that  in  spite  of  the  demand  for  H.S.  (high  speed)  steel  the 
market  for  Swedish  bar  in  Sheffield  is  not  particularly  brisk. 

The  ordinary  crucible  method  of  manufacture  is  used, 
and  the  necessary  proportions  of  the  ferro-alloys  are  added 
to  the  crucible  charge  of  converted  or  unconverted  bar. 
More  care  must  be  taken  in  the  melting  and  a  longer  time 
is  required  in  order  to  obtain  the  alloy  in  a  perfectly 
homogeneous  condition.  Many  of  the  imperfections  of 
high  speed  steels  of  which  users  complain  are  due  to 
imperfect  alloying.  The  pure  metals  themselves  could  not 
very  well  be  used,  even  if  they  could  be  produced  cheaply, 
on  account  of  their  high  melting  points.  As  the  ferro-alloys 
are  made  for  the  most  part  in  electric  furnaces,  it  is  probable 
that  H.S.  steel  will  also  be  produced  in  them,  and  it  is  diffi- 
cult to  understand  why  this  should  not  be,  for  excellent 
carbon  steel  is  so  made,  and  it  would  only  be  a  matter  of 
working  the  bath  of  steel  down  to  the  proper  content  of 
carbon,  and  then  adding  the  necessary  ferro-alloys.  Both 
the  Heroult  and  the  Kjellin  furnaces  should  give  good 
results. 

Most  of  the  methods  of  making  particular  brands  are 
supposed  to  be  secret,  but  the  following  details  of  a  process 
by  which  a  high-class  steel  is  made  is  a  refutation  of  the 
statement  that  only  Swedish  bar  can  be  used  : — 

70  Ibs.  of  scrap  tool  steel,  9  Ibs.  ferro-chromium,  and  14  Ibs. 
of  ferro-molybdenum  are  melted  together  in  a  crucible. 
When  the  charge  is  thoroughly  molten  170  Ibs.  of  molten 
steel  from  a  Tropena  converter  is  added  to  it,  together 
with  \  Ib.  of  aluminium.  The  full  charge,  when  ready,  is 


SPECIAL   STEELS.  347 

teemed  into  moulds  and  cast  into  ingots  4  inches  square, 
ready  for  the  usual  mechanical  treatment.  The  finished 
steel  contains  3  per  cent,  of  chromium  and  3  per  cent,  of 
molybdenum,  while  the  carbon  varies  from  0'75  to  0*9 
per  cent. 

The  ingots  of  H.S.  steel  are  reheated  to  a  temperature 
depending  upon  their  composition,  and  are  then  cogged 
down  under  a  steam  hammer.  When  cold,  the  hars  are 
examined  to  detect  any  defects,  reheated,  and  tilted  under 
small  hammers,  or  rolled,  into  the  required  sections. 
These  are  then  very  carefully  annealed  to  get  the  metal 
into  the  best  condition  for  working  up  into  tools,  and  to 
eliminate  the  internal  strains  set  up  during  the  tilting. 
The  tools  made  from  these  steels  should  be  annealed  after 
they  have  been  shaped,  preparatory  to  being  hardened. 
This  is  most  necessary  for  complicated  tools  such  as 
milling  cutters,  upon  which  much  labour  has  been  spent. 
The  internal  strains  are  thus  relieved,  and  the  tool  has  a 
much  better  chance  of  surviving  the  hardening  process. 

It  may  be  thought  that  H.S.  steel  requires  less  skill  in 
hardening  than  carbon  steel  from  the  fact  that  it  can  be 
raised  to  a  much  higher  temperature  without  injury,  but 
this  is  not  so,  for  special  precautions  must  be  taken  in  the 
high  heating  and  subsequent  cooling.  The  prescribed 
treatment  is  to  heat  slowly  up  to  812°  C.  (a  full  cherry-red) ; 
to  heat  rapidly  to  just  below  the  melting  point  (a  full 
white) ;  to  cool  rapidly  to  below  840°  C. ;  and  to  cool 
slowly  or  rapidly  to  the  temperature  of  the  air.  In  the 
low  heating,  or  tempering,  the  steel  is  raised  slowly  to 
612°  C.  and  kept  at  that  temperature  for  five  minutes ;  it  is 
then  cooled  rapidly  or  slowly.  A  double  muffle  furnace,  in 
which  the  upper  chamber  is  kept  at  about  812°  C.,  and  the 
lower  one  at  a  full  white  heat,  gives  excellent  results  for 
the  high  heating.  The  tools  are  put  on  the  top  of  the 
muffle  to  warm,  transferred  to  the  upper  chamber  to  soak, 


318 


IKON  AND   STEEL. 


and  then  to  the  lower  chamber  for  the  final  heating.  The 
rapid  cooling  is  usually  effected  in  a  blast  of  cold  air ;  but 
a  lead  bath  is  also  used  for  the  same  purpose.  The  low 
heating  is  best  carried  on  in  a  lead  bath  kept  at  a  tempera- 
ture of  612°  C. 

Makers,  however,  usually  issue  instructions  with  their 
steels,  and  these  should  be  faithfully  followed  if  the  metal 
is  to  have  a  fair  chance  of  doing  the  work  for  which  it  is 
intended.  Maltreatment  of  steel  by  the  user  is  the  steel 
maker's  greatest  source  of  trouble.  High  speed  steels 
may  be  described  as  iron-chromium-tungsten  alloys,  but 
molybdenum  and  vanadium  are  also  introduced.  Professor 
Howe  thinks  that  efforts  should  be  made  to  utilise  the 
more  abundant  elements  in  their  manufacture,  as  the 
supply  of  these  rare  elements  cannot  be  great,  and  may 
only  last  for  a  generation  or  so. 

The  following  table  contains  a  list  of  the  elements  found 
in  various  high  speed  steels  : — 

HIGH-SPEED  STEELS. 


English. 

American. 

Carbon,  C. 

1-00 

0-98 

1-85 

0-75 

0-674  ' 

1-13 

Silicon,  Si. 

0-06 

0-24 

0-15 

0-15 

0-043 

0-64 

Manganese,  Mn. 
Chromium,  Cr. 

0-50 
3-00 

3-10 

0-15 

2-00 

0-28 
3-00 

0-110 
5-470 

3-40 

Tungsten,  W. 

7-41 

8'50 

18-190 

Molybdenum,  Mo. 

6-00 

3-00 

3-90 

Vanadium,  V. 

0-290 

Molybdenum  has  the  same  general  effect   as   tungsten, 
but  is  more  active.     Two  per  cent,  of  the  former  is  said  to 


1  One  of  the  latest,  and,  according  to  Taylor,   one  of  the  best, 
American  H.S.  steels. 


SPECIAL  STEELS.  349 

be  equal  to  8  per  cent,  of  the  latter.  Also,  the  steel  only 
needs  to  be  raised  to  a  temperature  of  1,000°  C.  before 
being  air  quenched. 

It  will  be  seen  from  the  above  table  that  the  alloys  vary 
very  much  in  composition,  which  is  no  doubt  largely  due 
to  the  endeavours  of  the  various  makers  to  produce  alloys 
suitable  for  different  purposes,  and  for  undergoing  varying 
treatment  in  preparing  them  for  use. 

The  advantages  due  to  the  presence  of  tungsten  and 
molybdenum  are,  however,  quite  evident,  but  it  will  be 
noticed  that  the  influence  of  these  elements  is  always 
exerted  upon  the  iron  in  the  presence  of  carbon.  H.S. 
steels  of  any  value  contain  sufficient  carbon  to  harden  the 
iron  in  the  absence  of  the  other  elements.  The  influence 
of  these  elements  during  the  heat  treatment  of  the  alloys 
has  been  studied  by  Le  Chatelier,  Carpenter  and  others, 
and  appears  to  be  of  a  moderately  simple  character.  The 
temperature  range  in  which  marten  site,  the  hard  solid 
solution,  is  changed  into  pearlite,  the  soft  eutectoid,  is 
either  split  into  parts,  or  extended  downwards,  so  that  the 
martensite  is,  in  part  at  least,  preserved  down  to  the 
temperature  of  the  air.  The  alloy  is,  therefore,  hard, 
although  it  has  not  been  quenched  like  a  carbon  steel. 
Also,  according  to  Le  Chatelier,  on  reheating  hardened 
steel,  the  martensite  begins  to  segregate  at  200°  C.,  and 
tempering  takes  place  at  that  temperature ;  but  with  the 
H.S.  steel  the  segregation  does  not  commence  until  the 
temperature  reaches  nearly  600°  C.  The  result  is  that  this 
steel  will  preserve  its  hardness  and  "  stand  up  "  to  its  work 
even  when  it  is  red  hot.  When,  however,  the  steel  is 
raised  to  700°  C.  it  softens,  that  is,  the  carbon  change  takes 
place,  and  the  softening  goes  on  up  to  a  temperature  of 
850  to  900°  C.,  but  this  temperature  must  not  be  exceeded 
in  annealing.  Eaised  to  1,000°  C.,  or  above,  hardening 
again  takes  place.  Ease  in  hardening  and  resistance  to 


350  IRON  AND   STEEL. 

tempering  may  be  described  as  the  characteristics  of  these 
alloys. 

Many  practical  men  still  doubt  the  ability  of  H.S.  steel 
to  take  finishing  cuts  at  a  high  speed,  but  Gledhill  states 
that  an  excellent  finish  can  be  obtained  with  proper  tools 
suitably  arranged.  Thus  a  rolled  bar  can  be  finished  with 
a  good  bright  surface,  and  guaranteed  to  O002  inch  at  one 
cut. 

The  steel  for  chipping  chisels  has  its  wearing  property 
much  improved  by  the  introduction  of  0'25  per  cent,  of 
tungsten  ;  and  an  excellent  steel  used  for  making  permanent 
magnets  contains  from  5  to  6  per  cent,  of  that  element. 

An  important  series  of  experiments  were  carried  out 
during  October,  1903,  at  the  Manchester  Technical  School 
under  the  auspices  of  the  Manchester  Association  of 
Engineers,  and  a  detailed  account  of  them  published  in 
"  Engineering  "  for  April  3rd  and  16th,  1904.  Makers  were 
invited  to  send  their  special  brands  to  be  tested  in  the 
presence  of  their  own  representatives,  and  tools  made  from 
the  best  steels  on  the  market  were  used  in  the  trials.  These 
comprised  tests  of  endurance,  speed,  weight  of  metal 
removed,  area  machined,  depth  of  cut,  traverse  per 
revolution,  power  absorbed,  and  condition  of  the  tool  at  the 
end  of  the  trial.  The  most  important  result  of  the  investiga- 
tion is  that  the  same  steel  is  not  suitable  for  every  purpose 
to  which  high  speed  steel  can  be  put,  and  the  user  must 
trust  to  the  maker  to  supply  him  with  suitable  steel  for  a 
particular  tool.  Large  makers  take  every  precaution,  and 
have  special  shops  fitted  with  the  various  means  of  testing 
the  steels  they  supply.  Such  well  known  brands  as  Ajax, 
A.W.,  Novo,  and  Speedicut  are  guaranteed  to  do  certain 
kinds  of  work,  and  can  be  depended  upon. 

A  number  of  these  steels  were  tested  for  drilling,  boring, 
and  turning  by  a  Birmingham  engineering  firm  noted  for 
its  accurate  work,  and  it  was  proved  that  they  were  all 


SPECIAL  STEELS.  351 

superior  to  carbon  steel  for  the  particular  work  they  were 
put  to  do.  The  life  of  a  drill  was  10  times,  of  a  borer 
5  times,  and  of  a  turning  tool  3  times  that  of  the  ordinary 
steel  tool.  Hard,  medium  and  mild  steels  were  all  worked 
by  the  tools.  As  an  example  of  possibilities,  a  punch  |  inch 
diameter  punched  56,000  holes  in  structural  steel  as  against 
5,600  punched  by  an  ordinary  steel  punch  of  the  same 
dimensions. 

Manganese  Steel. — Manganese  in  small  quantity  is  always 
present  in  ingot  steel,  but  seems  to  have  no  decided 
influence  on  the  metal  when  under  1  per  cent.  This  is 
probably  due  to  its  being  engaged  in  neutralising  the  effects 
of  impurities,  and  preventing  red  shortness.  The  general 
effect  of  larger  quantities  is  to  harden  the  alloy  and  make  it 
brittle  ;  but  this  is  not  a  cumulative  effect,  for  the  brittleness 
increases  until  the  alloy  contains  between  4  and  5  per  cent, 
of  manganese,  and  then  decreases  as  the  percentage  of  the 
metal  increases  up  to  10  per  cent.  Alloys  containing 
between  2*5  and  7 '5  per  cent,  manganese  are  practically 
unworkable ;  while  alloys  containing  about  20  per  cent,  of 
manganese  resemble  cast  iron.  The  useful  proportions 
seem  to  lie  between  8  and  15  per  cent.  A  peculiarity  of 
these  alloys  is  that  when  heated  to  about  1,000°  C.,  and 
quenched  in  cold  water,  they  are  softened  and  toughened. 
They  can  be  forged,  but  are  so  hard  when  cold  that  they 
can  be  machined  on]y  with  great  difficulty,  which  con- 
siderably reduces  their  usefulness.  Most  of  the  information 
regarding  these  alloys  is  due  to  Mr.  Hadfield,  of  Sheffield, 
who  has  thoroughly  investigated  their  properties.  The 
well  known  Hadfield  manganese  steel  contains  about  13  per 
cent,  manganese  and  1  per  cent,  carbon,  and  has  a  tensile 
strength  of  upwards  of  60  tons  per  square  inch  ;  while  the 
elongation  is  nearly  50  per  cent.  The  tensile  strength  and 
ductility  of  these  alloys  are  increased  by  heating  to  a  white 
heat,  and  quenching  in  cold  water.  Manganese  steel  cannot 


352  IEON  AND   STEEL. 

be  magnetised,  and,  unlike  carbon  steel,  cools  from  a  red 
heat  without  showing  any  sign  of  recalescence.  It  is  used 
principally  for  rock  crushing  machinery,  railway  and  tram- 
way crossings,  and  safes,  its  great  hardness  and  ductility 
rendering  it  most  suitable  for  these  purposes. 

Nickel  Steel. — The  metal  nickel  is  now  put  on  the  market 
in  a  nearly  pure  state,  and  is  used  for  a  variety  of  purposes, 
one  of  which  is  to  alloy  with  iron  in  the  manufacture  of 
nickel  steel.  Either  the  metal  itself  or  the  rich  alloy  of 
ferro-nickel  may  be  employed,  and  must  be  added  to  the 
charge  in  the  furnace  on  account  of  its  high  melting  point. 
Also  it  is  necessary  to  add  ferro-manganese  at  the  end  of 
the  process,  as  nickel  is  much  the  same  as  iron  in  requiring 
a  deoxidising  agent.  The  alloy  is  cast  into  ingots  in  the 
usual  manner.  For  special  purposes  this  open  hearth 
product  may  be  re-melted  in  crucibles,  and  thus  rendered 
more  uniform. 

The  general  effect  of  nickel  on  the  steel  is  to  harden  it, 
but  not  to  the  same  extent  that  carbon  does ;  it  also 
increases  the  tensile  strength  and  elastic  limit  of  the  alloy 
without  seriously  reducing  its  elongation  under  tensile 
stress.  Such  a  steel  possesses  properties  well  suited  for 
making  forgings  for  engine  parts  that  require  great  tenacity 
and  high  elastic  limit  combined  with  sufficient  ductility 
to  prevent  them  giving  way  under  dynamic  stresses.  By 
using  this  alloy  the  weight  of  metal  in  the  parts  may  be 
reduced  with  safety,  which  is  sometimes  of  more  importance 
than  the  mere  cost  of  the  metal  when  lightness  combined 
with  strength  is  required.  About  12  per  cent,  of  nickel 
appears  to  be  the  limit  for  useful  work,  but  the  actual  pro- 
portion of  nickel  depends  upon  the  purpose  to  which  the 
alloy  is  to  be  put. 

The  following  table  is  abbreviated  from  the  table  recording 
Hadfield's  experiments  with  a  series  of  nickel  steels : — 


SPECIAL  STEELS. 


353 


Breaking  stress 

Elastic  limit 

Elongation 

Reduction 

in  tons  per 

in  tons  per 

per  cent,  on 

of  area 

square  inch. 

squaie  inch. 

2  inches. 

per  cent. 

" 

§ 

I 

"3 

1 

"rt 
C 

| 

1 

| 

1 

i 

a 

1 

1 

"3 

a 

1 

* 

|D 

^ 

(3 

£ 

3 

(3 

1 

()-14|o-75 
0-130-72 

0-27 
0-95 

31 
33 

28 

27 

19 
25 

20 
20 

35 
31 

37 
41 

56 
53 

52 
63 

0-19 

0-65    3-82 

37 

33 

28 

25 

30 

35 

54 

55 

0-17 

0-68 

7-65 

49 

45 

31 

30 

26 

26 

42 

41 

0-18 

0-9311-39 

94 

89 

65 

45 

12 

12 

24 

26 

0-19 

0-93  19-64 

91 

87 

47 

45 

7 

5 

6 

4 

0-14 

0-80 

29-07 

38 

37 

25 

16 

33 

48 

44 

51 

It  is  seen  from  the  table  that  the  breaking  stress  and  the 
elastic  limit  increase  with  the  content  of  nickel  up  to 
11*39  per  cent.,  and  then  decrease.  Also  that  these  two 
factors  increase  in  greater  proportion  than  the  elongation 
and  reduction  of  area  decrease.  Now,  since  the  percentage 
elongation  and  the  reduction  in  area,  particularly  the  latter, 
are  the  measure  of  tensile  ductility,  it  is  clear  that  greater 
strength  is  obtained  without  any  serious  sacrifice  of  tough- 
ness ;  and  these  are  the  principal  properties  of  a  metal  suitable 
for  resisting  comparatively  small  but  alternating  stresses 
such  as  occur  in  the  moving  parts  of  a  machine.  Thus  it 
is  largely  used  for  shafting,  connecting  rods,  crank  pins, 
piston  rods,  railway  axles,  and  tyres. 

Nickel  steel  used  for  gun  forgings  and  small  arms  barrels 
contains  about  0*2  per  cent,  of  carbon  and  3  per  cent,  of 
nickel.  Eeference  to  the  table  will  show  the  value  of  such 
an  alloy  for  this  purpose. 

Steel  containing  about  2  per  cent,  nickel,  1  per  cent, 
chromium,  and  0*4  per  cent,  carbon  is  being  largely  used 
for  armour  plates  and  armour-piercing  projectiles.  Nickel 
steel  containing  less  than  1  per  cent,  of  nickel  can  be 

1.8.  A  A 


354 


IRON  AND   STEEL. 


welded  as  readily  as  ordinary  steel,  but  with  higher 
percentages  the  welding  properties  decrease,  and  great  care 
is  required  even  with  the  3  per  cent,  alloy.  The  probable 
cause  of  this  is  the  tenacity  with  which  the  mixed  oxides 
seem  to  cling  to  the  heated  surface,  so  that  they  are  not 
completely  removed  by  the  fluxes.  According  to  some 
authorities  the  presence  of  nickel  in  the  higher  carbon 
steels  causes  a  lowering  of  the  recalescence  point,  so  that 
such  steels  can  be  both  annealed  and  hardened  at  lower 
temperatures  than  the  corresponding  carbon  steels. 

Vanadium  Steels. — As  already  mentioned,  vanadium  is 
sometimes  used  in  the  composition  of  H.S.  steels,  but  it 
does  not  appear  to  be  of  much  importance  in  this  connection. 
Although,  like  other  elements,  it  maybe  widely  distributed, 
it  does  not  occur  in  sufficient  quantity  to  bear  any  great 
drain  on  its  supplies.  Its  usefulness  seems  to  lie  more  in 
the  marked  influence  it  exerts  upon  ordinary  open  hearth 
steel  when  introduced  in  small  quantities,  together  with 
chromium.  The  effects  of  this  combination  on  the  physical 
and  mechanical  properties  of  constructional  steel  have  been 
under  careful  investigation  for  several  years  by  Captain 
Sankey,  Mr.  J.  Kent  Smith,  and  others,  and  their  tests 
point  to  the  very  great  importance  of  vanadium-chromium 
steels  for  constructive  material  that  is  to  be  exposed  to 
dynamic  stresses.  The  following  tensile  tests,  in  which 
open  hearth  steel  with  and  without  vanadium  are  compared, 
are  given  by  Mr.  Kent  Smith  : — 


Tenacity  in 

Elastic  limit 

Elongation 

Reduction 

tons  per 

in  tons  per 

per  cent,  on 

of  area 

square  inch. 

square  inch. 

2  inches. 

per  cent. 

Open  hearth  steel 

32-2 

17-7 

34 

52-6 

Open  hearth  steel,  with 

1  per  cent,  chromium 

and    O'lo    per    cent. 

vanadium 

52-6 

34-4 

25 

55-5 

SPECIAL   STEELS.  355 

The  results  of  these  tests  show  clearly  the  reason  for  the 
great  improvement  in  the  mechanical  properties  of  the 
steel  claimed  by  the  makers.  Mr.  Smith  is  of  opinion  that 
the  reduction  of  area  is  a  more  reliable  test  of  ductility 
than  the  elongation,  and  in  this  case  it  is  seen  that  with  a 
large  increase  in  the  breaking  stress  and  elastic  limit  the 
ductility  is  also  increased.  This  is  very  remarkable,  and 
if  it  will  stand  the  test  of  experience,  an  alloy  unrivalled  for 
a  variety  of  purposes  is  at  hand.  The  largest  makers  in 
this  country  at  present  are  Messrs.  Willans  and  Kobinson, 
and  they  are  said  to  be  exporting  their  products,  which  are 
almost  entirely  used  in  the  motor-car  industry.  The  alloy 
is  also  found  to  give  excellent  results  when  case-hardened, 
for  with  care  a  glass  hard  surface  on  a  tough  core  can  be 
obtained. 


A  A  2 


GLOSSARY 


ACIDS. — The  name  given  to  a  class  of  compounds  which,  when 
soluble  in  water,  furnish  solutions  having  a  sour  taste,  and 
capable  of  turning  vegetable  colours  red.  They  react 
with  bases  to  form  salts  by  which  their  acid  properties  are 
neutralised.  Some  acid-forming  oxides  are  insoluble  in 
water,  but  may  be  neutralised  by  fusion  with  basic  oxides, 
as  in  the  case  of  silica. 

AFTERBLOW. — The  term  used  in  basic  Bessemer  practice  to 
indicate  the  part  of  the  blow  after  the  removal  of  the 
silicon  and  carbon,  during  which  the  greater  part  of  the 
phosphorus  is  oxidised  and  passes  into  the  slag. 

ALLOTROPY  is  the  capability  of  some  elements  to  possess 
different  physical  properties  while  existing  in  the  same 
physical  state.  This  is  due  to  variations  in  the  number 
or  arrangement  of  the  atoms  in  the  molecules  of  the 
element,  or  of  the  grouping  of  the  molecules  themselves, 
by  which  the  internal  energy  is  increased  or  decreased. 
When  an  allotropic  change  occurs  it  is  always  accom- 
panied by  a  change  in  the  internal  energy,  and  takes  place 
at  a  critical  temperature. 

ALLOY. — A  mixture  of  metals  which  is  homogeneous  when 
fluid,  and  when  solid  possesses  the  physical  and  mechanical 
properties  of  a  metal.  Eich  iron  alloys  are  often  prepared 
direct  from  materials  containing  their  constituent  metals, 
and  these  products  are  used  in  making  alloys  for  industrial 


358  GLOSSAKY. 

purposes.  The  term  is  sometimes  applied  to  the  combina- 
tions of  iron  with  carbon  and  other  non-metals  when  a 
large  excess  of  iron  is  present. 

ARREST. — This  term  is  used  to  denote  a  stoppage  in  the  cooling 
or  heating  of  a  body,  which  is  due  to  an  internal  change 
taking  place  by  which  sufficient  heat  is  developed  or 
absorbed  to  counterbalance  that  lost  by  radiation  from  the 
body,  or  gained  from  the  source  of  heat.  The  duration  of 
the  arrest  depends  upon  the  magnitude  of  the  internal 
change.  In  the  heat  treatment  of  iron  and  steel  Ar. 
denotes  arrest  of  cooling,  and  Ac.  denotes  that  of  heating. 
These  arrests  do  not  take  place  at  the  same  temperature 
for  a  given  internal  change  on  account  of  the  "lag"  or 
disinclination  of  the  metal  to  change  its  state.  Thus  Ar.  is 
always  below  and  Ac.  above  the  critical  point. 

ATOMIC  THEORY. — This  conception  in  its  modern  form  was 
enunciated  by  Dalton  in  1808.  It  has  since  been  modified 
to  include  the  idea  of  molecules,  and  has  rendered  great 
service  in  the  development  of  theoretical  chemistry. 
Eecent  investigations  in  physical  chemistry  seem  to 
indicate  that  atoms  are  not  the  smallest  possible  particles 
of  elements,  but  are  built  up  of  still  smaller  particles 
called  "  electrons  "  when  charged  with  electricity,  or  simply 
corpuscles  when  not  charged. 

AUSTENITE. — The  name  given  to  a  constituent  of  hardened 
steel  in  honour  of  the  late  Sir  W.  Roberts-Austen. 

BASIC. — This  term  refers  principally  to  the  chemical  properties 
of  the  lower  oxides  and  hydroxides  of  the  metals,  by  which 
they  are  able  to  react  with  acids,  or  acid-forming  oxides, 
to  form  salts.  The  properties  of  both  are  merged  into 
those  of  the  salt,  which  has  distinctive  properties  of  its 
own.  Basic  oxides  soluble  in  water  give  solutions  that 
turn  red  litmus  blue,  and  have  a  caustic  action  on  the 
skin.  Basic  materials  contain  an  excess  of  basic  oxides. 

CEMENTITE  is  the  name  given  by  Howe  to  the  carbide  of  iron 


GLOSSAKY.  359 

Fe3C,  present  in  steel  and  cast  iron,  either  in  the  free 
state  or  in  the  eutectoid  pearlite.  It  furnishes  the  com- 
bined carbon  in  any  of  the  normal  forms  of  iron  and  steel 
containing  that  element. 

CHEMICAL  EQUIVALENTS  are  experimental  numbers  obtained 
by  determining  the  weights  of  the  various  elements  which 
unite  with  a  fixed  weight  of  one  element.  The  numbers 
are  sometimes  obtained  indirectly,  and  all  are  compared 
with  H  =  1. 

COLD  SHORT  is  applied  to  iron  and  steel  which  cannot  be 
hammered  or  rolled  cold  without  cracking.  Phosphorus  is 
the  most  hurtful  impurity  in  this  respect. 

CRITICAL  POINT  or  CRITICAL  TEMPERATURE. — This  is  fora  given 
change  a  definite  temperature  or  range  of  temperature  at 
which  or  within  which  the  change  takes  place.  When  the 
range  extends  over  several  degrees  of  temperature  it  is 
sometimes  called  a  zone. 

CRYSTAL  GRAINS. — Fragments  of  crystals  with  their  faces  and 
angles  either  absent  or  but  imperfectly  developed. 

CRYSTALS. — A  fully  developed  crystal  is  a  solid  of  definite 
geometrical  form  usually  bounded  by  planes  which  join 
each  other  and  form  solid  angles.  These  angles  are 
invariable  for  a  particular  crystalline  form  which  enables 
crystals  to  be  recognised,  and  classified  into  systems. 
Iron  in  common  with  other  metals  crystallises  in  cubes, 
and  so  belongs  to  the  cubic  system.  Ferrite  grains  are 
more  or  less  cuboidal  in  form. 

CURVES. — When  there  are  two  variables  connected  with  a 
change,  and  they  can  be  measured  as  the  change  proceeds, 
the  change  may  be  represented  by  a  diagram.  The  vari- 
ables are  measured  on  two  reference  lines  or  co-ordinates, 
which  are  usually  at  right  angles,  and  cut  each  other  in  a 
point  called  the  origin,  see  Fig.  73.  Thus  if  the  variables 
are  time  and  temperature,  as  in  cooling,  the  temperature, 
at  a  given  moment,  can  be  indicated  by  a  point  on  the 


360  GLOSSAKY. 

vertical  reference  line,  or  on  any  line  parallel  to  it,  and  the 
time  on  the  horizontal  line,  or  any  line  parallel  to  it. 
Therefore  the  temperature  of  the  body  at  any  given  time 
will  be  represented  by  a  point  on  the  surface  where  these 
lines  cut.  Thus  by  noting  the  temperature  of  a  cooling 
body  at  equal  intervals  of  time,  plotting  the  points  on  the 
diagram  and  joining  them,  a  continuous  line  is  obtained. 
If  the  fall  in  temperature  is  strictly  proportional  to  the 
time  the  line  will  be  straight,  but  if  not  it  will  be  curved. 
Cooling,  stress  and  strain,  etc.,  may  be  represented 
graphically  in  this  way,  and  the  greater  the  number  of 
points  determined  the  more  accurate  the  curve  will  be. 

DYNAMICS. — The  branch  of  mechanical  science  that  deals  with 
bodies  in  motion. 

ENDOTHERMIC  as  applied  to  chemical  change  denotes  that  as 
the  change  takes  place  heat  is  absorbed  into  the  reacting 
system,  and  unless  heat  is  supplied  from  outside  the  tem- 
perature of  the  system  will  fall  below  that  at  which  the 
change  is  possible.  The  temperature  must  therefore  be 
maintained  above  this  critical  point  if  the  change  is  to 
go  on. 

ETCHING. — The  name  given  to  the  differential  action  of  a 
solvent  liquid,  or  other  agent,  on  a  surface  not  perfectly 
homogeneous. 

EUTECTIC  is  the  general  term  used  by  Guthrie  to  denote  a 
mixture  of  two  substances  having  a  lower  melting  point 
than  any  other  mixture  of  the  same  two  bodies.  Among 
the  mixtures  of  two  metals  the  one  containing  the  eutectic 
proportions  is  the  eutectic  alloy.  When  solid  it  is  called 
the  eutectic  mixture,  and  when  liquid  the  eutectic  solution. 
If  the  melting  points  of  a  series  of  the  alloys  of  two  metals 
are  plotted  on  a  diagram  the  lowest  point  on  the  curve 
indicates  the  melting  point  of  the  eutectic  alloy,  and  a 
horizontal  line  drawn  through  this  point  is  termed  the 
eutectic  line.  See  Fig.  74. 


GLOSSAEY.  361 

EXOTHERMIC. — The  large  majority  of  chemical  changes  are  such 
that  heat  is  developed  as  they  proceed.  When  once  in 
progress  the  change  goes  on  as  long  as  the  reacting  bodies 
are  present  in  the  system.  As  heat  is  constantly  leaving 
the  system  the  change  is  regarded  as  a  source  of  heat,  or 
exothermic. 

FERRITE. — The  name  given  to  pure  iron  as  it  is  seen  in  cuboidal 
grains  under  the  microscope,  and  to  carbonless  iron,  which 
may  contain  silicon,  manganese,  etc.,  in  solid  solution.  In 
the  case  of  silicon  it  may  be  called  silico-ferrite. 

FLUX  is  the  general  term  used  to  denote  the  solid  material 
added  to  a  smelting  mixture  to  remove  the  earthy  matter 
as  a  fluid  slag.  A  basic  flax  is  required  for  an  acid  gangue, 
and  vice  versa.  Lime,  magnesia,  alumina,  and  oxide  of 
iron  are  the  common  basic  fluxes  used  on  the  large  scale ; 
but  soda  and  potash,  as  carbonates,  are  used  for  assays. 
Silica  or  siliceous  matter  is  the  acid  flux,  but  borax  is  often 
used  on  the  small  scale. 

FUSIBILITY  expresses  the  fact  that  a  body  can  pass  from  the  solid 
to  the  liquid  state  when  heated,  and  the  more  readily  it  fuses 
the  more  fusible  it  is  said  to  be.  Some  bodies  have  definite 
fusing  points,  that  is,  the  temperature  range  within  which 
they  are  both  solid  and  liquid  is  a  comparatively  short  one. 
The  metals  are  good  examples  of  such  bodies.  On  the 
other  hand,  slags  and  similar  bodies  have  no  definite  fusing 
points,  for  they  pass  through  a  long  range  of  temperature 
without  any  decided  arrest,  such  as  is  present  in  the 
heating  curve  of  a  metal. 

HARDENITE. — A  term  used  by  Charpy  and  Howe  to  denote  the 
solid  solution  of  iron  and  carbide  containing  O9  per  cent, 
of  carbon. 

HELICAL  (from  helix,  a  spiral). — This  is  usually  applied  to 
pinions  that  come  into  action  gradually  with  a  sliding 
motion.  The  teeth  are  so  formed  that  when  one  pair  of 
teeth  are  parting  company  the  next  pair  are  just  coming 


362  GLOSSARY. 

into  contact,  and  the  motion  is  uniform  throughout.  The 
bumping  inseparable  from  heavy  cog-wheels  with  few  teeth 
is  thus  avoided. 

HYPEREUTECTIC  is  used  to  designate  steels  containing  more 
than  O9  per  cent,  of  carbon. 

HYPOEUTECTIC  is  used  to  designate  steels  containing  less  than 
O9  per  cent,  of  carbon. 

INTEEPENETRATION  is  a  kind  of  mutual  nitration  of  one  sub- 
stance into  another.  It  is  usually  applied  to  the  mingling 
of  the  particles  of  two  solid  masses  in  contact,  to  the 
passage  of  solid  particles  into  a  plastic  mass,  and  of  molten 
matter  between  the  faces  of  crystals. 

METASTABLE  indicates  the  condition  of  a  substance  when  its 
temperature  is  below  or  above  that  at  which  it  should 
pass  into  another  form,  but  is  prevented  from  so  doing  by 
its  own  molecular  inertia.  In  the  case  of  allotropic  change 
the  metastable  body  is  either  above  or  below  the  transition 
point. 

NEUTRAL,  as  applied  to  oxy-salts,  means  that  the  acid  and  basic 
properties  of  their  constituent  oxides  have  been  completely 
merged  into  the  properties  of  the  salts.  In  the  case  of  fire- 
resisting  materials  it  means  that  they  resist  the  fluxing 
action  of  acid  and  basic  oxides. 

OCCLUSION. — When  metals  absorb  gases  and  retain  them  in 
the  solid  state  they  are  said  to  occlude  the  gases.  As  this 
gaseous  matter  is  capable  of  reappearing  with  its  original 
tension,  it  may  considerably  affect  the  mechanical  pro- 
perties of  the  metals,  and  is  a  constant  source  of  blow- 
holes. Iron  is  capable  of  absorbing  carbon  monoxide, 
hydrogen,  nitrogen,  etc. 

PEARLITE. — The  name  given  by  Howe  to  the  pearly  constituent 
of  steel  discovered  by  Sorby.  It  is  the  eutectoid  of 
ferrite  and  cementite  present  in  annealed  steel,  white  cast 
iron,  etc. 

BED  SHORT,  as  applied  to  iron  and  steel,  means  that  the  metal 


GLOSSAEY.  363 

is  unworkable  at  a  red  heat.  Copper,  sulphur,  and  oxide 
of  iron  render  the  metal  red  short  or  hot  short  when 
present  in  sufficient  quantity. 

KEGENERATION. — A  term  applied  by  Siemens  to  the  restoration 
of  heat  carried  away  from  a  furnace  by  the  gases  on  their 
way  to  the  chimney.  The  heat  is  absorbed  by  refractory 
brickwork,  reabsorbed  by  the  entering  gases,  and  so  carried 
back  to  the  furnace. 

EEVERBERATION  is  the  beating  back  of  the  flame  and  products 
of  combustion  by  a  properly  constructed  roof  to  heat 
materials  placed  on  the  bed  of  the  furnace.  Eadiation 
from  the  low  roof  also  plays  an  important  part  in  the 
heating. 

EUSTING. — A  term  now  generally  applied  to  the  surface  changes 
taking  place  when  a  metal  is  exposed  to  the  atmosphere. 
The  change  taking  place  is  an  oxidising  one,  and  iron 
among  the  common  metals  is  most  prone  to  it.  The 
protection  of  iron  and  steel  from  rusting  when  it  is  to  be 
exposed  to  the  air  is  of  great  importance.  In  most  cases 
the  film  of  oxide  first  formed  protects  the  metal  under- 
neath from  further  action,  but  this  is  not  so  with  iron,  for 
the  rusting  eats  right  to  the  heart  of  the  metal,  so  that  the 
air  must  be  entirely  excluded  for  the  protection  to  be 
effective.  The  means  adopted  depend  upon  what  the 
metal  is  to  be  used  for.  The  coating  of  tin  on  ordinary 
tin  plate  is  very  effective.  To  do  this  the  iron  sheets  are 
carefully  cleansed  from  scale  by  pickling  in  dilute  sulphuric 
acid  and  scouring.  They  are  dried  by  immersion  in  molten 
tallow,  and  are  then  passed  through  a  series  of  pots  con- 
taining molten  tin,  by  which  they  are  coated  uniformly 
with  a  thin  layer  of  the  metal.  In  some  cases  the  surface 
of  the  sheets  is  improved  by  passing  them  through  rolls 
after  immersion  in  the  last  tin  pot.  The  zincing  of  sheets 
and  pipes  is  also  largely  carried  on  for  the  production  of 
galvanised  iron.  The  operation  is  somewhat  similar  to  the 


364  GLOSSARY. 

process  of  tinning,  for  the  surface  to  be  coated  is  thoroughly 
cleansed  from  scale  and  the  sheet  plunged  into  a  bath  of 
molten  zinc  covered  with  sal-ammoniac.  The  zinc  alloys 
with  the  iron  and  forms  a  good  coherent  coating,  which  is 
very  effective  unless  the  iron  becomes  exposed  in  any 
part.  In  that  case  the  rusting  is  even  more  rapid  than 
usual,  due,  probably,  to  electrical  action.  Iron  coated 
with  zinc  by  electro-deposition  is  now  being  put  on  the 
market  under  the  name  of  Sherradised  iron.  In  the  Bower- 
Barff  process  the  iron  is  first  heated  in  the  flame  of 
producer  gas,  and  then  exposed  to  the  action  of  super- 
heated steam,  by  which  a  coating  of  the  black  oxide  is 
formed  on  the  surface  and  effectively  protects  it  from  rust. 
Painting,  varnishing,  and  greasing  are  also  resorted  to  for 
the  prevention  of  rusting. 

SEGREGATION.— The  more  fusible  portions  of  alloys  are  driven 
inwards  as  the  mass  solidifies,  and  tend  to  accumulate  in 
the  part  which  solidifies  last. 

SOLID  SOLUTION. — According  to  Van-t-Hoff  a  solid  solution 
is  a  homogeneous  mixture  in  the  solid  state,  and  may  be 
either  crystalline  or  non-crystalline  in  character. 

SOLUTION. — A  solution  is  a  homogeneous  mixture  of  two  or 
more  bodies  in  the  liquid  state  which  do  not  separate 
from  each  other  under  normal  conditions. 

STATICS. — The  branch  of  mechanical  science  which  deals  with 
the  action  of  forces  on  bodies  at  rest. 

SURFUSION. — The  condition  of  a  liquid  which  has  passed 
through  its  normal  freezing  point  without  becoming 
solid. 

TEMPERATURE. — The  condition  of  a  body  with  regard  to  the 
tendency  of  heat  to  escape  from  it.  The  greater  this 
tendency  the  higher  the  temperature  is  said  to  be.  Solids 
and  liquids  that  will  withstand  a  high  temperature 
become  incandescent  as  their  temperature  increases,  thus 
giving  out  light  as  well  as  heat,  and  the  appearance 


GLOSSAEY.  365 

of  a  solid  gives  a  rough  indication  of  its  temperature. 
Thus  an  incipient  red  heat  is  about  500 ;  red,  700 ; 
bright  red,  800—1,000;  white,  1,300;  dazzling  white, 
1,500°  C. 

THE  EGGERTZ'  TEST  is  a  colour  method  for  determining  the 
percentage  of  combined  carbon  in  iron  and  steel.  The 
metal  is  dissolved  in  dilute  nitric  acid,  and  a  solution 
having  a  brown  colour  is  obtained.  This  is  then  compared 
with  a  similar  solution  in  which  the  same  weight  of  a 
standard  steel  has  been  dissolved.  The  standard  solu- 
tion is  poured  into  a  measuring  tube  and  diluted  with 
water  to  a  known  volume ;  the  solution  under  examination 
is  treated  in  the  same  manner,  and  diluted  until  the  depth 
of  colour  in  the  two  tubes  is  exactly  the  same.  The 
volumes  are  then  noted,  and  the  assay  is  finished.  The 
volumes  are  directly  proportional  to  the  percentages  of 
combined  carbon  in  the  standard  and  in  the  sample,  and 
since  the  one  is  known  the  other  is  easily  calculated. 

TRANSITION  POINT. — The  point  through  which  a  body  passes  on 
changing  from  one  form  or  state  to  another  as  it  is  heated 
or  cooled. 


INDEX 


A. 

ABEL,  Sir  F.,  277 

Acid-forming  oxides.  8 

Acids,  8,  357 

Afterblow,  74,  357 

Air,  variations  in  the,  92 

Allen,  231 

Allotropy,  286 

Alloy,  357 

Alloys,  iron,  103 

Alternator,  321 

Aluminium  in  iron,  230 

Ampere,  the,  322 

Annealing,  307 

Anthracite,  24 

Arnold,  J.  O.,  230,  267,  272,  278 

Arrest,  286,  358 

Arsenic  in  iron,  283 

Atmosphere,  the,  11 

,,  composition  of,  12 

Atom,  4 
Atomic  theory,  4,  358 

„       weight,  4 
Austenite,  279 

B. 

BASIC,  358 

,,      bottom,  173 


Basic  lining,  172 
,,      materials,  46 
,,      oxides,  8 
Batho  furnace,  199 
Bauxite,  48 
Bedson,  248 
Belgian  mill,  247 
Bell,  Sir  I.  L.,  63 
Bellamy,  C.  V.,  63 
Bergman,  140 
Bertrand-Thiel  process,  211 
Bessemer  process,  acid,  159 
,,  ,,        basic,  170 

,,         slag,  acid,  169 
,,  ,,     basic,  177 

,,         steel,  uses  of,  181 
Best  tap,  133 
Billet,  244 

Black  heart  castings,  310 
Blair  process,  62 
Blast  furnace  changes,  85 
,,          ,,         charging,  91,  101 

gas,  91 

,,          ,,         modern,  74 
,,          ,,         plant,  85 
,,          ,,         practice,  100 
slags,  89 
the,  68 
„     hot,  93 
,,     pressure  of,  96 


368 


INDEX. 


Blast  stove,  modern,  80 

,,     temperature  of,  96 

„     the,  79 
Blister  bar,  143 
Bloom,  244 
Bloomery,  American,  57 

high,  58 

Blooming  shears,  243 
Blooms,  treatment  of,  214 
Blowing  cylinder,  83 

,,       engines,  83,  163 
Blue  billy,  132 
Boilings,  131 
Breaking  stress,  254 
Brinnel,  307 
Bull  dog,  132 

C. 

CALCINATION,  69 

,,  in  kilns,  71 

in  stalls,  71 
Calcining  kiln,  72 
Calcium  chloride,  204 
fluoride,  204 
Calorific  intensity,  29 
,,         power,  24 

table  of,  29 
Calorimeter,   Berthelot  -  Mahler, 

27 

,,  Thompson's,  25 

Campbell  tilting  furnace,  205 
Carbon,  allotropic   modifications 

of,  286 

,,       dioxide,  7 
,,       monoxide,  7 
,,       solution  of,  in  iron,  291 
Carbonate  ores,  17 
Carpenter,  349 
Case  hardening,  153 
Casting  ladle,  178 


Castings,  black  heart,  310 

malleable,  112 
Catalan  process,  55 
Cementation  process,  142 
Cementite,  276 
Charcoal,  31 
Charger,  electric,  207 
Charging,  cup  and  cone,  91 
Chemical  equation,  6 

„        equivalents,  4,  359 
Chenot  process,  The,  61 
Chocks,  238 
Chrome  iron  ore,  49 
Cinder,  iron,  52,  57,  117,  131 
„       notch,  77,  123 
„       pig,  106 
Clay,  144 

,,     wheel  forge,  216 
Clough,  134 
Coal,  22 

,,     sulphur  in,  31 
,,     testing  of,  24 
Cogging,  244 
Coke,  32 
, ,      average  composition  of,  32 

oven,  33 
Cold  blast  iron,  107 

,,     short,  359 
Combining  proportions,  4 
Concentration,  73 
Converter,  Bessemer,  159 

bottom,  160 
,,  concentric,  161 

,,  eccentric,  162 

Eobert,  the,  180 
small,  178 
Cooling  curves,  copper  and  iron, 

285 
,,  ,,        iron-carbon,  297 

lead-tin,  289 
,,       salt  solution,  291 


INDEX. 


Copper  in  iron,  283 

Cort,  119 

Cowper,  80 

Critical  point,  359 

Crucible  steel,  141,  145 
,.  ,,       melting,  146 

,,  ,,       uses  of,  155 

Crucibles  for  steel  melting,  146 

Crushing,  resistance  to,  261 

Crystal  grains,  268 

Cup  and  cone,  91 

Cupola,  foundry,  the,  113 

Curves,  359 

Cylinder,  the  blowing,  83 

D. 

DALTON,  atomic  theory  of,  4,  358 

Danks'  furnace,  135 

Darby,  67 

Dellwik,  42 

Deoxidisers,  230 

Despretz,  324 

Dewar,  285 

Dick,  200 

Dolomite,  47 

Drop  test,  265 

Ductility,  256 

Dud  Dudley,  67 

Duff-Whitfield  producer,  40 

Dust  catcher,  76 

Dynamics,  360 

Dynamo,  319 

E. 

EASTWOOD,  134 
Eggertz  test,  197,  365 
Ekrnan,  237 
Elasticity,  255 

„          modulus  of,  256 
Elastic  limit,  255 


Electric  furnace,  steel  making  in, 

326 

Elements,  table  of,  13 
Endothermic,  37,  360 
Equalisers,  97 
Equation,  chemical,  6 
Equivalents,  chemical,  4,  3.59 
Etching,  271 

,,         solutions  for,  271 
Eutectic,  288 

,,         alloy,  289 
Eutectoid,  298 
Exothermic,  361 
Eye,  furnace,  78 


F. 


FERRITE,  275,  361 
Ferro-chromium,  103 

,,      manganese,  103,  336 

,,      silicon,  103,  338 
Eery,  318 
Fettling,  124 
Firth,  Messrs.,  251 
Fleischer,  42 
Fluor  spar,  204 
Fluxes,  85,  104,  361 
Foster,  W.  J.,  95 
Foundry  irons,  analyses  of,  108, 

109,  110 

,,         practice,  110 
Fore  plate,  123,  239 
Forge  hardening,  304 

„       Pig,  131 
„       rolls,  221 
Fuel,  21 

,,      gaseous,  35 
Furnace,  blast,  68 
,,         charge,  88 

Danks,  the,  135 
electric,  324 


I.S. 


B  B 


370 


INDEX. 


Furnace  eye,  78 

Heroult,  the,  327,  329 
Husgafvel,  the,  59 
Keller,  the,  337 
Kjellin,  the,  330 
Muffle,  308 
,,         obstructions,  99 
,,         Osmund,  the,  58 
,,         Pernot,  136 

puddling,  123 
,,         reheating,  222 
,,         reverberatory,  119 
,,         revolving,  135 
,,         Stassano,  the,  332 
,,         tapping  the,  97 
,,         tilting,  205 
Fusibility,  361 

,,         of  silicates,  44 


G. 

GANGUE,  16 

Gannister,  46 

Gaseous  fuel,  35 

Gases,  occlusion  of,  228 

Gas  furnaces  for  puddling,  138 

„     Mond,  38 

,,     producers,  37 

,,     suction,  42 

,,     waste,  80 

,,     water,  38 
Gibbs,  295 
Gjers,  72 

,,       soaking  pits,  233 
Gledhill,  J.  M.,  345 
Grant,  Colonel,  63 
Graphite,  48,  279 
Gooseneck,  78 
Guides,  239 
Gysinge  Bruk,  331 


H. 

|  HAANEL,  Dr.,  339 
Hadfield,  351  852, 
Haematite,  brown,  17 

red,  17 
Hall,  J.,  122 
Hammer,  helve,  214 
,,          refining,  309 
,,          scale,  133 
slag,  132 
steam,  218 
tilt,  215 

Harbord,  211,  235 
Hardening,  300 
Hardenite,  279,  361 
Harmet,  M.,  232 
Harrison,  97 
Harvey  process,  the,  154 
Hearth,  Swedish  Lancashire,  116 
Heat,  dissipation  of,  301 
,,      refining,  309 
,,      tinting,  273 
Helical  pinion,  240,  361 
Heroult  process,  326 
Heyn,  281 

Hiorns,  A.  H.,  275,  280 
Hot  blast,  93 

,,       ,,       theory  of,  94 
Housing,  239 

Howe,  57,  167,  284,  298,  309,  348 
Huntsman,  145 
Husgafvel  process,  59 
Hypereutectic,  362 
Hypoeutectic,  362 


INGOT  metal,  treatment  of,  226 

,,      moulds,  166 
Interpenetration,  362 


INDEX. 


371 


Iron,  allotropic  modifications  of, 

288 

,,     chloride  of,  18 
,,     cold  blast,  107 
,,     for  the  foundry,  108 
,,     making  in  Africa,  63 
„  India,  52 
„     mill,  216 
,,     ores,  16 

,,       ,,      concentration  of,  73 
,,       ,,      distribution  of,  19 
,,       ,,      occurrence  of,  16 
,,       ,,      preparation  of,  69 
„       „      table  of,  '21 
,,     pig,  104 
„     pure,  1 
,,     pyrites,  17 
,,     red  oxide  of,  3 
,,     rusting  of,  2 
,,     stone,  blackband,  17 

„       clay,  17,  71 
,,     sulphides  of,  17 


JOULE,  323 


J. 


K. 


KELLER  furnace,  the,  337 
Kent  Smith,  354 
Kilowatt,  the,  323 
Kjellin  process,  the,  329 

L. 

LA  PRAZ,  328 
Ladle,  casting,  164 
„      tilting,  164 
Le  Chatelier,  293,  314,  349 


Ledebur,  310 
Lens,  273 
Lester,  I.  E.,  54 
Lignite,  23 
Limestone,  47 
Lining,  basic,  172 
Loam  moulding,  115 
Low  Moor,  107 

M. 

MACHINE,  casting,  102 

slag,  98 

,,        tensile  testing,  257 
,,        transverse  ,,      262 
Magnesite,  47 
Magnetite,  16 
Malleable  castings,  112 
Martin,  E.  P.,  171 
Martensite,  278,  298 
Massel,  151 

Materials,  refractory,  43 
Mechanical  puddling,  134 

,,          treatment,  214 
Merchant  bar,  221 
Metastable,  362 
Microscope,  the,  273 
Mill,  continuous,  the,  242 

„     furnace,  the,  223 

,,     iron,  the,  214 

,,     looping,  243 

„     pull  over,  240 

,,     reversing,  241 

,,     train,  225 

„     three  high,  242 
Miller,  68 
Molecule,  4 
Molybdenite,  49 
Mond  gas,  38,  42 
Mould,  ingot,  166 
Moulding,  114 

B  B  2 


372 


INDEX. 


Moissan,  285 
Molybdenum,  348 
Mushet,  K.,  157,  343 


N. 

NANIA  BATHAN,  54 
Native,  16 
Neutral,  362 

,,       materials,  48 


0. 


OCCLUSION  of  gases,  228 
Ohm,  the,  322 
Ohm's  law,  322 
Oil  baths,  306 
Open  hearth  process,  182 
pig,  196,  202 
,,         ,,        practice,  198 
,,         ,,         refining  in,  195 
„         ,,        regenerative,  188 

slags,  196,  202 

,,         ,,        steel,  uses  of,  213 
,,         .,        Styrian,  150 
tap  hole,  184 
,,          ,,         working  a  charge  in, 

200 

Ore,  non-phosphoric,  20 
,,     phosphoric,  21 
,,     winning  the,  19 
Ores  of  rare  metals,  49 
Osmond,  287,  293 
Osmund  furnace,  the,  58 


P. 

PEARLITE,  277 

Pernot  furnace,  the,  136 


Peel,  190,  223 
Phase  rule,  the,  294 
Phosphoric  oxide,  9 
Pickles,  134 
Pig  bed,  98 

Pig  iron,  acid,  168,  196 
„      „     basic,  178,  202 
.,      ,,     grading  of,  106 
,,       „     grey,  106 
„      ,,     hungry,  124 
,,      ,,     mottled,  106 
,,      ,,     Styrian,  152 
,,      ,,     Swedish,  158 
,,      ,,     white,  106 
,,      ,,     world's  output  of,  107 
Pile,  charcoal,  31 
Pinion,  helical,  240 
Pipe,  227 
Plasticity,  45 
Plate  rolling,  245 
Plumbago,  48 
Pottery  mine,  133 
Press,  forging  the,  251 

,,       Whitworth,  the,  231 
Process  Bertrand-Thiel,  the,  211 
,,       Bessemer,  the,  156 

Blair,  the,  62 
,,        Catalan,  the,  55 
,,        open  hearth,  the,  182 
,,        puddling,  the,  119 

South  Wales,  the,  118 
Talbot,  the,  209 
Producer,  Duff-Whitfield,  the,  40 

gas,  37 
,,        Siemens,  the,  39 

Wilson,  the,  39 
Puddled  balls,  treatment  of,  216 

„       bar,  221 
Puddling  furnace,  123 
,,        mechanical,  134 
,,        process,  119 


INDEX. 


373 


Puddling  process,  changes  in,  125 

,,  ,,         modern,  122 

Pull-over  mill,  240 
Pyrometer,  radiation,  the,  316 
,,          resistance,  the,  312 
,,          thermo-electric,   the, 
313 

Q. 
QUENCHING  liquids,  300 


B. 

BAIL  rolling,  245 

Recalescence,  288 

Red  short,  362 

Reduction,  10 

Refining  in  the  open  hearth,  195 

Refractory  materials,  43 

,,  „          acid,  46 

„  „          basic,  46 

,,  ,,          neutral,  48 

table  of,  46 

Regeneration,  363 

Reheating  furnace.  234 

,,  ,,         gas  fired,  235 

Reverberation,  363 

Reversing  mill,  241 

Revolving  furnace,  135 

Richards,  W.,  93,  171 

Riley,  200 

Robert  converter,  the,  180 

Roberts-Austen,  299,  314,  324 

Rod  rolling,  247 

Rogers,  J.,  120 

Rolling  mill,  237,  253 

Rolls,  222 

,,     two  high,  237 

Roozeboom,  299 


Rotator,  Siemens,  the,  138 
Running  out  fire,  120 
Rusting,  363 


S. 

SANKEY,  Captain,  267 

Sauveur,  298,  300 

Scaffold,  100 

Segregation,  228,  364 

Sexton,  H.,  90 

Shackles,  261 

Siemens,  Sir  W.,  324 
,,  process,  189 
,,  rotator,  62 

Silica,  8 

Silicates,  table  of,  44 

Silicon,  8 

„       in  iron,  281 

Skids,  241 

Slag,  acid  Bessemer,  169 
„     basic        ,,          177 
,,     acid  open  hearth,  196 
,,      basic    ,,         „        202 
,,     blast  furnace,  89 
„     pocket,  189 
,,     scouring,  89 
„     wool,  98 

Slab,  244 

Slip,  100 

Smelting  of  pig  iron,  74 

Snelus,  127,  170 

Soaking  pits,  233 

Solution,  solid,  291 

Sorby,  277 

Sorbite,  300 

South  Wales  process,  118 

Specific  heat,  311 

Spiegeleisen,  103 

Squeezers,  220 


374 


INDEX. 


Stalls .  calcination  in,  71 
Stassano  process,  the,  333 
Stead,  J.  E.,  171,  267,  276,  277, 

308 
Steel,  forging,  250 

,,      high  speed,  348 

„      manganese,  351 

„      Mushet,  344 

„      nickel,  352 

„      rolling,  245 

,,      self-hardening,  343 

„      special,  343 

„      Styrian,  150 

,,      Vanadium,  344 
Stopper  hole,  123 
Stove,  hot  blast,  the,  81 
Strength,  tensile,  257 

„  transverse,  262 
Stresses,  alternating,  266 
Sulphur,  9 

„       allotropic  modifications 

of,  287 

„        in  coal,  31 
Symbol,  4 


T. 


TABLE  of  acid  materials,  46 
„       „     basic         ,,         48 
„       ,,     blast  furnace  charges,  90 
,,       ,,     calorific  power,  29 
„       „     clay  ironstone,  71 
„       „     elements,  13 
„       ,,     iron  ores,  21 
,,       ,,     oxides,  13 
,,       „     puddling  furnace 

charges,  133 
,,       ,,     silicates,  44 
„       ,,     tempering        tempera- 
tures, 305 


Talbot  process,  209 

,,      continuous  furnace,  237 
Tap  hole,  77,  184 
Tapping,  97,  131,  193 
Teeming,  147 
Temper  carbon,  310 
Temperature,    measurement    of, 

311 

table  of,  305 
Tempering,  300,  305 
Tenacity,  254 
Test  bars,  260 
Testing    dynamic,  264 

,,         machine,      "Wicksteed's, 

258 

Tilters,  241 
Tilting  furnace,  205 

„       ladle,  164 
Tin,  allotropic   modifications  of. 

287 

Torsion,  resistance  to,  261 
Transition  point,  287,  365 
Transverse  strength,  262 
Treatment  of  ingot  metal,  226 

„  puddled  balls,  216 
Tucker,  A.,  235 
Turner,  Prof.,  93,  131, 133 
Twyer,  blast  furnace,  78 
Tympstone,  77 


U. 


UEHLING,  102 

Ulverstone,  68 


V. 

VANADIUM  steel,  354 
Vanadinite,  50 


INDEX. 


Vein  stuff,  16 
Volt,  the.  322 


W. 

WATER,  10 

„        gas,  38,  42 
,,       twyer,  78 
Walloon  process,  118 
Walrand-Legenissel  process,  180 
Washed  metal,  137 
Watt,  the,  323 
Weathering,  73 
Weld  iron,  118,  141 
„     steel,  141,  145 
Welding.  253 

electric,  342 
Wellman  furnace,  206 


Whitworth,  Sir  J.,  232 
press,  231 
Wicksteed,  258 
Wild  heat,  230 

„     metal,  230 
Wire  drawing,  248 
Wolframite,  49 


YIELD  point,  257 
Yorkshire  bar  iron,  138 
Young's  modulus,  256 

Z. 

ZINCING,  364 

Zone  of  combustion,  86 


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